28
The Histoey and Control
of Sex.
David M. Mottier.
The student
of sex
tionally ask himself
and
any or
ra-
the following questions
the
all of
why
significance of sex? or, in other \A-ords,
Is the sex of the
individual? or
may
What is
closely related problems of heredity
:
are organisms male and female?
organism determined during the early development of the
is it
predetermined in the germ cells?
what
If the former,
conditions of the environment are favorable to the development of males
and what
to females?
If the latter,
what
is it in
the gametes or sex-cells
that predetermines maleness or femaleness?
As
in the establishinent of the doctrine of sexuality itself, these ques-
answered by exjjeriment only and by the microscopic investiga-
tions can be
germ
tion of the
duction to what
cells
I
and the manner of
shall
have to say
As an
their development.
in this
intro-
paper concerning sex control,
desire to pohit out briefly those lines of study
which seem
to
me
to
been most effective in establishing the doctrine of sexuality in plants
it
will be seen that the lines of investigation
I
have
;
for
which established the theory
of sex are similar to those that are yielding the most fruitful results in
the study of the more difficult hereditary problems of the present day.
When
in rhe history of civilized or semi-civilized
that plants possess sex, no one can
tell
man, the idea arose
or perhaps imagine.
Before the
days of written history the old Arabs of the desert knew that certain palm
trees produced fruit, while others did not, and,
miglit develop abundantly,
it
was necessary
in order that the fruit
to bring the flowers of the
sterile trees
and hang them upon the branches of those which bore the
fruit.
evident that they also practiced the caprification of the
It is
fig,
using the same methods employed at the present time in the fig-growing
localities along the Mediteri-anean, for
ing of the Babylonians, states that.
we read
in
"The natives
Herodotus who,
tie
in
speak-
the fruit of the male
palms, as thej- are called by the Greeks, to the branches of the date-bearing
palm, to
let
fruit falling
the gall-fly enter the dates and ripen them, and to prevent the
off.
The male palms,
like the wild fig trees,
have usually the
29
Herodotus was
gall-fly in their fruit."
of the gall
fly in
the palm, and
it
is
error in regard to the presence
in
said that Theophrastus
said,
is
he knew six hundred plants.
this subject
seemed
"it is certain,"
more
to he
Let
the botanists of
little
to the
him
tiie
and 17th centuries considered the rudiment
KJth
knowledge of
either
upon natural
history.
sexualit,\' in
Tliat he
parent from the following
date-palm does not
is
of the
by
shaken
fig,
and
o\'er
seemed
to
have made no observations upon
it
:
"What men say
])erfect itself unless the
it,
is
the
blossom of the male wath
indeed wonderful, but
nuuds of educated men.
lation between the
Now
not
is
In the time of Pliny,
had been pretty well confirmed
in
In his "Historia Mundi,"' in describing the re-
male and female date-palm, Pliny
the material of fertilization, and says that naturalists
and even herbs have the two
its
resembles the caprification
it
the perfecting of the foetus."
this idea of sexual difference in plants
ap-
is
that the fruit of the female
might almost be concluded that the female plant
itself sufficient for
down
plants whicli had been handed
the subject, but to have relied in a large measure upon heresay,
dust
of
Theophrastus probably added very
form of tradition or through the scanty writings
the
in
female
jialms, for instance, bear flowers, the
be borne in mind here that neither Theophrastus nor
it
the fruit to be a part of the flower.
to
some male and some female, for
he says, "that among plants of the same species some produce
and some do not; male
only fruit."
He
than those of his great teacher.
definite
and terebinths as being
regards the paln\
flowers
first
was probably the foremost of all ancient botanists, for,
The ideas of Theophrastus upon
pui)il of Aristotle
it
was the
This brilliant and gifted
to point out the inaccuracy in the statement.
calls the pollen-dust
tell
us that
all trees
sexes.
while the ancients had soine notion of sex in plants, their ideas
wei*e based chiefly
upon certain apparent analogies with animals.
It
must
be borne in mind that whilst the ancients attributed to the pollen the power
of fertilization, they
had no notion that
this
fertilization
was anything
further than some unexplained subtile influence of the flower dust upon
the fruit.
However,
A\e
should wonder only at
how much they knew
in
the days of Herodotus and Theoithrastus as compared with the progress
of
knowledge made along this
yeax's: for the
line
during the following two thousand
time from Aristotle to the discovery of the
cell
by Robert
Hooke, the publication of the great works on anatomy by Malpighi and
Grew, and the experiments of Camerarius
century,
was
a
in the latter
part of the 17th
lapse of long and dreary centuries in the history of science.
30
This was not because there were no
men
willing to devote their time to
natural history, but chiefly because of the attitude of mind which de-
manded that problems
arising be not solved by observation and experi-
ment, but by the process of deductions from the authorities.
tion
was
not,
what do the observed
interpreted from
what
The improvement
facts toacli?
Init.
how
The
ques-
are they to be
Aristotle says?
of the microscojie and the extensive studies on the
minute anatomy of plants did not bring the results that might have been
In spite of his excellent work on the anatomy of
reasonably expected.
plants,
Grew seemed
have been unable to gain any true insight into the
to
He
structure and function of pollen.
the so-called male
attire,
Sir
members
did not even consider the stamens as
them only as the
of the Uower, spealcing of
unknown
but he records a conversation with an otherwise
Thomas
Millington.
who was probably
stamens the character of male organs.
Plants" (chap. V, sees. 3 and
page 171)
4.
learned Saviliau professor, Sir
Thomas
the
I
:
first
botanist.
person to claim for the
quote from the "Anatomy of
"In discourse hereof with our
Millington. he told
me
he conceived
that the attire doth .serve as the male for the generation of the seed.
immediately replied that
sons for
it
1
was
of the
same opinion and gave him some
h'.s
But
and answered some objections which might oppose them."
how badly Grew must have been confused
in the
matter
may
be seen from
He
description of the florets in the head of certain Composit;«.
garded the style and stigma of the
floral attire
I
rea-
re-
as a portion of the male
organ, speaking of the small globulets (pollen grains) in the thecae (anthers) of the seedlike attire as a vegetable sperm which falls upon the seed
case and so "touches
in plants
it
with a
Grew could
prolific virtue."
conceive of sex
only in the form of certain apparent analogies with animals.
reasoned that the same plant
and some other animals are
may
be both male and female, because
He
.snails
so constituted, but to complete the similarity
between the plant and the animal would require that the plant should not
only resemble the animal, but should actually be one.
1091. about all that
was known concerning the
Down
to the
sexuality in plants
year
was com-
piised in the facts related by Theophrastus for the date-palm and the terebinth,
and
in the conjectures of Millington,
pighi's views in opposition to these authors
Grew and
others, while Mal-
were considered equally well
founded.
The
doctrine of sexuality in plants could only be raised to the rank
of scientific fact by experiment.
It
was necessary
to
show that no seed
oi
capable of germination could
fonued without
lie
historic records concur in proving that
first to
tlie
aid of polleu. and
all
Rudolph Jacob Camerarius was the
attempt to solve the problem in this way.
Dioecious plants were
cultivated a])art from each other, but no perfect seeds were formed.
removed the stamens from the flowers of the castor
oil
He
plant and the
stigmas from maize, with the result that no seeds were set in the castor
oil plant,
and
The
seen.
empty husks were to be
Camerarius were published in 1691-94. At this time
in the place of grains of corn only
results of
the authority of the ancients
\A'as
so great that Camerarius thought
it
neces-
sary to insist that the Aiews of Aristotle and Theophrastus were not op-
Among
posed to the sexual theory.
next
fiftj-
an Irishman by
I
Logan experimented with some plants of maize.
birth.
pon a cob from which
as
many
the few experiments carried out in the
years were those of the Governor of Pennsylvania, James Logan,
lie
removed some of the stigmas, or
grains as there were stigmas remaining.
he found
silks,
One cob which was
wi-apped in muslin before the silks appeared, produced no kernels.
Gleditsch, director of the botanic garden in Berlin,
had been
In ITol,
told that a
date palm eighty years old, which had been brought from Africa, never
bore fruit.
As there was no
itsch ordered pollen sent
staniinate tree ot the species in Berlin, Gled-
from
I^eipzig.
The journey required nine
and although Gleditsch thought the pollen
was hung upon the Berlin
germinated
tree,
spoiled, the
days,
male inflorescence
with the result that seeds were set which
in the following spring.
The century following the discovery
of
Camerarius was characterized
by two lines of investigation which, more than any other activity of botcomplete establishment of the sexual theory.
anists, led to the
I
refer to
the refutation of the old theory of evolution together with the birth of the
doctrine of epigenesis, and the discovery of hybridization
;
the
first
of these
being the outcome of microscopic studies, and the latter that of experimentation.
It
may
be said in this connection that the history of biological
science teaches that the greatest
been
made where
liave
gone on side by
According
germ
to
and the most substantial progress has
the studies of the morphologist and of the experimenter
side, the
one serving as a control upon the other.
the old theory of evolution, or the inclusion theory, that the
in every seed, for example, contained all the parts of the organism,
and that this germ enclosed a similar one
box within a box.
in miniature,
and
so on. like a
This view of the inclusion of germ within germ was
veiy prevalent in the 18th century, and Kaspar Friedrich Wolf (1759) has
32
been given the credit of refutiug:
it.
Wolf, in his doctor's thesis on the
"Theory of Generation," maintained that the embryo and organs of a phint
dfveloi) not by the unfolding of parts already present in miniature, but
that they grew out of inidiffereutiated rudiments, the theory of epigenesis.
However. Wolfs argimients were far from convincing, as he held that the
was merely another form
act of fertilization
of nutrition.
Al)out the .same time experiments in hybridization were being carried
on by several investigators, and the results obtained supplied
much more
Among
convincing i)roof against the old theory of evolution.
the fore-
most men
in this heltl
Sprengel.
While Kolreuter brought together many important observations
were Gottlieb Koelreuter
and Christian Konrad
on the sexuality of plants, yet his greatest service consisted
In this connection
tion of hybrids.
first
may
it
hybrids were produced between two species of tobacco plants.
and
tinna puiiicinn
A',
What he accomplished
rnstica.
when combined with
ing changed, but
belong to our time.
not always these,
It
were capable of producing hybrids, and that the mingling
was no easy matter
was the
best refutation of the theory
to place the proper estimate
value of the contributions of this gifted observer.
Linnaean
century,
has been used in
His work seems to
Koelreuter showed that only closely allied plants, and
of parent;!; characters in the hybrid
of evolution.
Xico-
did not require be-
later observations
the discovery of general principles of hj'bridization.
tle
in the protluc-
be of interest to note that his
The
upon the
collectors of the
school, as well as the true systematists at the close of the IStli
who wielded
a r.owerful infliuence upon botanical thought,
had
lit-
understanding for such labors as Koelreuter's. and incorrect ideas of
hybrids prevailed
in spite of
botanical literature.
Hybrids were also incon-
venient for the believers in the constancy of species.
Koelreuter's studies were not contined to hybridization alone, for he directs attention to the natural
way
of the transfer of pollen from stamen
to stigma, being the first to recognize the
showing that
pollen grains,
fertilization
agency of
insects.
He
studied
followed pollenation in the ab-
sence of light, and rejected the idea that the pollen grain passed bodily
into the ovary.
With the microscope,
howcA-er, he
as an experimenter, for he supposed the pollen
the fertilizing substance to be
and
finds its
way
oil
to tlie ovule.
gr.-iin
which adheres
The
was
than
less skillful
to be solid tissue, and
to the outside of the
grain
pollen tulie had not been discovered,
although the time was one hundred years after the discovery of the
by Robert Hooke.
cell
;
33
As Camerarius
showed that
first
proved the sexuality of plants, aud Koelreuter
different spec-ies can
unite sexually to produce hybrids, so
Sprengel demonstrated that a certain kind of hybridization was very com-
mon
kingdom, namely the crossing of tlowers of different
in the vegetable
individuals of the
same
To him belongs
species.
shown the part played by
the credit for having
insects in cross pollenation,
first
and pointing out the
correlation between such properties of the flower as color, odor, nectar,
special forms
and markings, and so
and the
forth,
visiting insects.
Karl Friederick Gaertner, son of Joseph Gaertuer, took up the work so
ably begun by Koelreuter, and greatly extended the knowledge of hybridi-
His
having kept accurate account of nine thousand experiments.
zation,
work was published
in 1849.
more confirmed the existence
manner that
in ISGO,
it
which
Sachs states that "These observations once
of the sexuality in plants,
could never again be disputed.
led to the
certain individuals of
When
and
facts
in
such a
were observed
presumption that under certain circumstances
some
species of plants, the fejuale organs
in
might pro-
duce embryos capable ot development without the help of the male, there
was no thought
of using these cases of supposed parthenogenesis to dis-
prove the existence of sexuality as the general rule
only to verify
see
first
how they were
isting
ideas
of
;
men were concerned
of all the occurrence of the phenomena,
to be
and then
to
reasonably understood side by side with the exGaertner's experiments
sexuality."
were conducted
at
Claw, in Wurtemberg, the place in which Koelreuter carried on his studies
Camerarius worked
in Tiibingeu.
While the experimenters
with the microscope was no
in
hybridization were at work, the student
less busy.
In 1823, Amici discovered the pollen
tube in the stigma, and the fact was confirmed by others.
same observer traced the pollen tube
into
the
ovule.
In 1830, the
Schleiden
and
Schacht now came forward with their erroneous theory of the formation
of the
embyro
in the seed.
They maintained that
from the end of the pollen tube after the
clear tliat this doctrine
the
embyro develops
latter enters the ovule.
would do away with the
It is
essential point in the
sexuality of plants, for the ovule would be regarded merely as an incu-
bator for the embyro.
Amici, in 184G, brought forth decisive proof for the
view he had maintained, namely, that the embryo arises not from the end
ol the pollen tube, but
from a portion of the ovule which already existed
before fertilization, and that this part
[8—18192]
is
fertilized
by a
fluid
contained
in
34
polleu tube.
tlio
year
bj'
The correctness
of
tliis
view was coutirmed the followiug
von Mohl aud Hofuieister, the hitter of
in detail wiiicli decided
the question,
whom
and illustrated
described the points
tlieni
with beautltul
figures.
FolluwiuL? the )»ublication of Aniici, a vehi'uient controversy arose be-
tween the adberents of the views
ottered by
an essay by
trated
Institute of
tlie
tlie
ot Schleiden
Xetlierlauds at
Scliaclit in 1850, wliich
aud those
A
uf Amici.
prize
Amsterdam was awarded
defended Schleidens theory, and
to
illus-
by a numl)er of drawhigs giving both incorrect and inconceivable
it
futed before
it
was reVon Mohl's
In this case the prize essay
representations of the decisive points.
appeared, by von Mohl, Hofmeister and Tulasue.
words uttered
in ]M>3 in regartl to the value of prize essays are so fitting
at the present
day that
He
can uot refrain front quoting.
I
that we know that Schleiden"s doctrine was an
but at the same time sad, to see
said
:
"Now
illusion, it is instructive,
how ready men were
to accept the false
for the true; some, renouncing all ob.servation of their own, dressed
phantom
the
in theoretical principles; others
but led astray by their
j
up
with the microscope in hand,
irecouceptious, believed that they
saw what they
could not have seen, and endeavored to exhibit the correctness of Schleiden"s notions as raised above all doubt by the aid of hundreds of figures,
which had everything but truth
to
recommend them; and how an academy
by rewarding such work gave fresh confirmation to an experience which
had been
re])eated]y
made good
especially in our
years past, namely, that prize essays are
little
own
subject during manj-
adapted to contribute to
the solution of a doubtful question in science."
The discovery
of the sexual process in crypttjgams by Thuret, Priugs-
heim and others followed within four or
five
years after the complete
establislnneiit of that process in the higher plants.
now
us
its
til
that a
phenomenon
occui-rence
had been
so easy of
cojupletely demonstrated in
ing the greatest dilhculties to
its
investigation.
est to recall that just thirty-two years
tial
It
observation was
seems strange to
jiot
discovered un-
organisms present-
However,
it
is
of inter-
ago Strasburger traced the essen-
constituents of the nucleus in unbroken sequence from one
cell
genera-
tion TO another, thus establishing for the nucleus the rank of niori)liological unity;
and just thirty-two years ago also Oscar Ilertwig showed that
consists essentially in the union of the two gamete nuclei.
fertilization
It
only remained
now
for later studies on the cell to confirm
lish the doctrine that the
nucleus
is
and
to estab-
the bearer of the heredity characters.
35
With
this
we
view,
is
now ready
are
some
to consider
modern
of the
phases of our subject.
Any
related
Consequently,
I
shall
does not exist, and
sex
development of
effort to trace the
phenomena would
sexual reproductive
is
are
scarcely
The
cells.
male and female.
and
also simple,
details.
to
with a sexual process, the
be distinguished
conclusion
is
There
cells.
from the non-
that gametes were originally
'I'he life cycle of
accordingly no ditferen-
is
these simple sexual plants
reasonable to suppose that a corresponding degree
is
it
all cor-
tlie
in the simplest plants
tliat,
derived from a sexual propagative
tiation into
sexual pi-ocess with
an overwhelming mass of
merely recall that among the lowest plants sexuality
gametes,
or
cells,
lead us into
of differentiation obtains in the chromatin or hereditary substances of tae
sex
cells.
As we ascend
complex organisms, we
tures and functions,
stance, or
a
is
man
in the broadest
—or
may
and most fundamental
I/ow then did sex come about?
one individual or member of a
To ask such questions
regarded as visionary.
point, the
is
of a secondary nature
fifty or
life
I
say maleness and femaleness
sense.
And what
cycle will be
is
it
that determines that
male and another female?
even twenty-five years ago might have been
Not so today. Considered from the botanical stand-
problem of sex determination has to deal with a certain category
phenomena that are
many
in
respects tundamentally different from those
presented by animals. In plants in which sex differentiation
there
is in
every com] ilete
life cycle
is
well defined,
two phases known as the sexual and the
asexual, or gametophyte and sporophyte.
fertilized
There-
has ascribed to the individuals of his own species, but that
of a purely hereditary character
of
struc-
very fundamental sort of division of labor.
do not mean by that a division of labor which
such as
all
also that the hereditary sub-
likewise specialized and differentiated?
fore, sex is the expression of a
I
corresponding differentiation in
and may we not assume
germ plasm,
toward higher and more
in the scale of e^'olution
find
egg or the union of sex
cells.
The
.sporophyte springs from the
This sporophyte in turn bears
This may be made clear by means
The spores borne on the leaves of the fern
spores which give rise to gametophytes.
of an
example such as the
fern.
do not jjroduce directly new ferns, but very
thallia,
which
dividuals.
in
The
.small
plants
known
as pro-
the simpler ferns are independent and self-nourishing inprothallia are the sexual plants.
gans, which
is
either purely
male or female or hermaphrodite.
turn produce eggs and sperms.
They bear the sex
or-
may
be
The
When
prothallia
the egg
is fertilized
36
it
develops immediately into the sporophyte. or what
Thns the sexual
the fern.
we commonly know
as
gametophyte (female gametophyte)
plant, or
not only produces the sex organs, but serves as the incubator and brooder
The
young sporophyte.
for the
of the highest plants such as
life-cycle
and sunflowers consists also
trees
two generations, but the
of these
and mutual relation of sporophyte and gametophyte are
tive size
For example, the beech tree
in the higher plants.
gametophyte being the
is
the sporophyte, the
tube and the embryosac of the undeveloped
jiollen
Here the reverse condition prevails as regards the mutual
seed.
rela-
different
relation
of sporophjrte and gametophyte to that in the fern, namely, the sporophyte
nourishes the young sporophyte as well as both gametophytes.
Now, we are
the habit of speaking of male and female flowers
in
according as they are wholly staminate or
we
bears only staminate flowers
tillate
flowers
call
However,
designated as the female individual.
is
morphological sense the sporophyte
strict
and the plant that
pistillate,
male, while the one bearing only pis-
is
in the
without sex. hence trees can
be neither male nor female, and to avoid trouble and useless discussion,
it
is
doubtless better to speak of staminate and pistillate trees
shall see that the sex of
the germ
cells.
From
any complete
the foregoing
kingdom, apart from one or two
life-history that is
We
are
to
nearly
ters are
When
all
is
and
generations, there
is
nothing in the
biologists concur in the
in the
diffei*-
Our explanation
sporophji;e depend?
based upon the theory of the hereditary substance.
borne by a substance
of
Doubt-
view that the hereditary charac-
nucleus of the
cell
called chromatin.
the nucleus divides the chromatin differentiates tnto a definite num-
ber of pieces
known
The number
as chromosomes.
always constant for the reproductive
any
cells of
of the sporophyte of any plant, which lie in the
of
species.
germ
mation of spores, however,
each spore has
n,
the
reduced
is
chromosomes, and the
sulting therefrom will possess
the sperm will have each
and sperm
number
;/,
n.,
In
all
is
the cells
n.
to
During the
for-
one-half, or
iu.
the gametophyte re-
chromosomes: consequently the egg and
chromosomes.
unite, the fecundated egg
will contain h, plus n. or
cells of
chromosomes
tract, there are. let
us say. a definite number of chromosomes designated by
Now
in
quite clear that in the animal
answer the question, upon what does the
entiation into gametophyte
less
it
we
for
;
determined and fixed
comparable to sporophyte and gametophyte.
now ready
this doctrine is
cell
life-cycle is
It is
apparent that when egg
and the individual arising from
n chromosomes.
it
37
The most fuudamenta]
difference between sporophyte
the fact that the latter possess just one-half as
lies in
and gametophyte
many chromosomes
This hereditary difference between sporophyte and gameto-
as the former.
phyte and the change which brings about the transition
by means of the following
the chi'omatin.
Fig.
nary vegetative
cell.
illustrates the behavior of the
1
may
be
made
clear
showing diagramatically the behavior of
figure,
chromatin
Here the chromatin segments passing
in
an ordi-
into the
nuclei are formed by a longitudinal fission of a single chromosome
equational division.
sion in spore
In Fig.
mother
cells.
2,
a to
/,
is
shown the
first
new
—an
or reducing divi-
One-half of the somatic chromosomes pass to
one of the daughter nuclei and the other half to the other, thus bringing
about
tlie
mother
cell
reduction of the number.
(/;
to
/)
is
The second
division
in
the spore
equational.
Fig.
1.
Diagrams showing: the behavior of the chromatinlduring: an ordinary somatic
showing chromatin'distributed in small granules
within the linin networli and a nucleolus, b. the chromatin spirem has formed and it has
split longitudinally, c. the spirem has segmented into chromosomes, e. g., eight, d. spindle stage; chromosomes arranged in the equatorial plate, e. anaphase; daughter chromo
somes moving toward the poles of the spindle, f. daughter nuclei, each containing
eight daughter chromosomes. Such a division is known as equational, since the two reFigr.
1.
mitosis, a. nucleus in resting condition,
sulting nuclei are hereditarily
The
parallel between plants
of the reduced
tliat in
alilie.
number
of
and animals
chromosomes
is
found in the phenomenon
in the sex-cells,
with this distinction,
higher plants the reduction in the number of the chromosomes oc-
38
curs
when
may
the spores are formed, which
while
differentiated;
animals the reducti<m immediately precedes the
in
In regard to the chromosomes themselves, the
formation of the gametes.
view generally prevailing
viduality which
is
many thousands of cell
when eggs and sperms are
be
generations remo^e<l from the time in ontogeny
is
that each possess a distinct identity or indi-
maintained throughout ontogeny, and phenomena per-
taining thereto have been presented under the theory of the individuality
Very
of-the chromosomes.
recently, however, the idea of individuality has
been taken away from the chromosomes and applied to smaller units, such
as the eliromonu'res. or better the microscoi)ical]y distinguishable granules
which make
or select
chromomeres.
tlie
ui«
writer has expi'essed
m;iy call tht'se particles pangens,
a
as a fuller discussion
The
views on this subject
liis
and only
publication,
ence.
We
any name which may be convenient and
few brief statements
is
The
will be
made
here, in as
much
regarded as being too technical for a general audi-
idea of individuality
is apjilied to
particles comi)Osing them, chielly because
is
likely of adoption.
in greater detail in a recent
the chromomeres or the small
tlie
identity of the
chromosome
'There are no good reasons to believe that
lost in the i-estin nucleus.
a given chromosome always contains the same hereditary qualities in any
succession of
Furthermore, no special importance should
generations.
cell
be attached to the different
si5:GS
of the
chromosomes,
of the most striking jihenomena in a dividing nucleus
ence in the size
the chromosonn'S.
v.f
is
for,
as a rule, one
the marked differ-
These small material
particles, or
pangens, are responsible for the characters of the individual, although they
are not regarded as
tlie
immediate characters themselves.
They may be
roughly compared with ferments, bringing about changes which collectively
constitute
development, and produce those
which form,
nuclei,
ture.
color,
and so
re-arrangements of
<-heiiiicaI
forth, are the visible expression.
Fused gamete
however, do not constitute a chemical union but a mechanical mix-
The numerical reduction
a condition of sexuality.
It
is
of the
chromosomes
is
a
consequence and
probably not a mere halving of the bulk of
the chromatin, but a selection and a distribution between daughter cells of
structural entities— the primordia
one generation
to
another.
of characters
The Mendeliaii
anything worth while, that these units
therefore, directs
and controls
ai-t
cytei)lasm.
shows,
independently.
cellular de\elopiiient.
tions known as variation are probably due
and
which are handed from
jirinciple
if
The
it
shows
nucleus,
The outer manifesta-
to the inter action of nucleus
39
Fig.
2.
Fig. 2. Diagrams illustrating the behavior of the chromatin during the
tion divisions in a spore mother cell.
a~f. first or heterotypic mitosis,
two matura-
a. resting
longitudinally split chromatin spirem developed from a;
the halves of the spirem are twisted upon each other, c, spirem has segmented into
eight chromosomes which have approximated in pairs to form the four bivalent chromosomes. These eight chromosomes were united end to end in the spirem of b, just as in
the ordinary somatic mitosis, d. spindle with the four bivalent chromosomes arranged
in the equatorial plate, e. anaphase, the four chromosomes retreating towards the poles
of the spindle. Each of these retreating chromosomes is now more clearly seen to be
composed of two halves which were formed by the longitudinal splitting in b. f. daughter nuclei in which the spirems will be formed by the union end to end of the daughter
segments. This is the division in which the number of chromosomes is reduced to onehalf, because whole chromosomes pass to each daughter nucleus. If these whole chromosomes are different in hereditary characters, the division is qualitative or differential.
Q—i- second or homotypic mitosis, g. spindle showing the four chromosomes arranged
in the equatorial plate; the free ends of the daughter segments of each chromosome
diverge from each other, h. the segments passing to the poles of the spindle, i. the
grand-daiighter nuclei resulting from the second mitosis. This is an equasional division,
because it consists of the separation of half chromosomes, or daughter segments, formed
by the longitudinal fission of whole chromosomes.
niicleus,
same as
in
fig.
1.
h.
40
In speaking of sex. let us bear iu
plants there
may
miud that among both animals and
be three kinds of individuals:
Dioecious
the individuals are unisexual, either male or female
bisexual or hermaphrodite individuals
;
;
and parthenogenetic,
tors of the environment, or
sex
cells,
tors,
and
i.
in either
e.,
that which
is
it
in the case of plants,
it
is
sorts or
take
Of the environmental
is
fac-
nutrition,
probably the only one that need be consid-
and
heat, are only influ-
But we should
ential in so far as they affect nutrition.
we have two
in-
determined by fac-
supposed to play the most important role
is
which
predetermined in the chromatin of the
sperm or egg or both?
ered, for other important factors, such as light
that
is
in
We may now
dividuals pi'oduce eggs that develop without fecundation.
up the question, vvliether the sex of the individual
which
sijecies, in
monoecious, with
also understand
In
two categories of environmental conditions.
case the fecundated egg develops wholly apart from the parental body, and
as a completely independent individual, its supply of nourishment
the external world
tilized
is
from
but in those cases iu which the incubation of the
;
fer-
egg and the early development of the embyro take place within the
parental body, the food supply will depend upon the condition of the parent.
it
AVhile the conditions of these
two categories seem very
different, yet
will be found that the final results are essentially the same.
For the sake of
will be mentioned.
simplicity, a
few instances from the animal kingdom
Experiments were carried on by Riley and others
to
determine whether the starring of caterpillars of butterfles might influence
the number of males and females
.
possible, says Kiley, to
urally.
The
make
normal conditions of nutri-
for under
tion the catei-pillars produce both juales
and females, and because
caterpillars take
results of the ex])eriments
of
many
Zool., p. 377)
Upon
makes the following statement:
of these experiments has
now become
shown that the sex of the caterpillar
the egg. Under these circumstances
produce a change in the sex.
It is
not
nat-
showed that an excess or diminu-
tion of food does not alter the proportion of the sexes.
Morgan (Exp.
it is
more food than they do
apparent, since
is
already determined
it
is
this point
"The
futility
has been
it
when
it
leaves
not probable that feeding could
much more
probable that starvation or
overfeeding could only affect the proportion of males and females by bringing about a greater mortality of the individuals of one sex."
studies have been
Cuneot upon
flies
made
ui)on the
and moths,
silk
worm by
Numerous
Kellog and Bell, and by
to determine the influence of food conditions
upon the sex of the individual and upon that of the egg and sperm, with
:
41
the conclusion that the sex
is
not determinerl by external conditions. While
the preponderance of evidence along this line seems to argue strongly
against any influence upon sex-determination by food conditions,
is
there
j-et
one case, that of Hydatena senta and the daphnid, Simocephalus. investi-
gated by Nussbaum and others, in which
might have some determining influence.
seemed probable that food
it
Maupas, on the other hand,
garded temperature and not food as the influential factor.
nection, the studies of vo]i
Malsen (Archiv.
upon a small worm, Dinophihis apatris, and
daphnids, are of especial interest.
mikr. Anat., 69:
f.
re-
In this con-
of Issakowitsch
6.3-97.
1906.)
(Idem) upon
Malsen found that a higher tem-
\'on
perature (26^ C) was favorable to the development of males, while a lower
He
temperature gave an increased ratio of females.
change
ing
tlie
nutrition of
the animal
iiroduced,
1.
e..
of food at the disposal of
at the higher temperature, the sexual ac-
the rapidity with which a large
was abnormally
insuflicient for the
The amount
animal.
tlie
was the same, but
tivity of the animal.
was
does not attribute the
in the sex ratio to the temi)erature directly, but indirectly as affect-
number
of eggs
accelerated, so that the bodily nutrition
proper nourishment of the eggs.
Consequeutlj',
higher temperaUire a larger number of eggs are produced, and
them
is
a proportionately large number of smaller or male eggs.
was
at a
among
At a
lower temperature, on the contrary, repi'oductive activity was slower, and
among the smaller number
ished female eggs was the
ment of these
To
of eggs developed, a larger ratio of well nourresult.
There was more time for the develop-
and consequently more food placed at their
eggs,
estimate the value of these statements
in
warm and
the
is
disposal.
necessary to examine the
The number
data niwn which the conclusions are based.
and the sexual ratio
it
cool cultures are
of eggs considered
shown
in the fol-
lowing tables
NORMAL.
No. of Eggs.
1140
Male.
Female.
327
813
Number
of eggs at each laying,
Ratio of Male
:
Female.
:
Female.
1:2.4
5.6.
COOL.
No. of Eggs.
3948
Male.
973
Number
Female.
Ratio of Male
1:3.5
2975
of eggs at each laying,
4.2.
42
WARM.
A
0.
of Eggs.
Male.
female.
507
880
1393
Number
Female.
:
1:1.7
of eggs at eacli lajang,
At the higher temperatures
Ratio of Male
3.6.
coumlonl.^ happened that the eggs were
it
developed so rapidly that the bod}' of the animal
was
entirely filled
from
one end to the other, the head appearing as a smalliwint, the intestine
so compressed as to be scarcely Aisible.
unable to move and soon perishes.
a larger
number
should be accepted with
In the
of error.
much
From
alone would not be a
In the second place
fall
marked variation
it
in the size
would seem that
accurate method of determining the
strictly
does not seem improbable that, at higher tem-
it
and with a more rapid generative
peratures,
would
the very
from his own measurements,
of the female eggs, as given
size
von Malsen's conclusions
size of the eggs alone, the large ones representing fe-
males, the smaller eggs males.
sexes.
that
reserve, because of certain probable sources
he seemed to have based his estimate of males
first i^iace
and females upon the
me
seems to
It
therefore,
produced so rapidly that the body can not
of eggs are
properly nourish them.
In this condition the animal is
At the higher temperature,
as prey to the larger eggs
;
activity,
fewer smaller eggs
for in these animals the larger
female eggs are frequently nourished at the expense of the smaller.
nutritive activity of these large eggs
is
If the
increased proportionately to the
sexual activity by higher temperature, then the larger eggs should consume
the smaller ones in like ratio
this to be true.
It
may
:
but von Malsen does not seem to have shown
be said that at lower temperatures the larger
female eggs have relatively more time in which to consume the smaller,
hence fewer small, or male, eggs are
The question then
laid.
arises, does
von Malsen's experiments prove that higher temperature leads to the production of
that,
more female than male eggs from the generative
at a higher temperature,
tissue? or merely
ot the relatively larger
produced, a proportionately smaller number of male eggs
number
is
of eggs
consumed
in
the nutrition of the female eggs.
The researches
of Issakowitsch
with a different class of data.
upon
a
daphnid bring us face to face
This author reared
thi^
descendants of
parthenogenetic females through several generations (six as a
and found that the production of females
ture
(24°
is i)aralleled
maximum),
with high tempera-
C). and that the males with lower temperature, the
direct
43
worm
opposite to that which happened in the
Issakowitsch
Diuophilus.
sliows that tenii)eratui'e acted merely as iiitiueiicing uutritiou, for
animals were starved by
being-
From
eggs were deA'eloped
his experiments
it
parthenogenetic eggs were concerned, nutrition
ing factor.
Botli
when
the
reared in distilled water, males and resting
would seem
may
that, so far as
act as a sex-determin-
von JMalsen and Issakowitsch look upon nutrition as a
sex-determining factor from the influence
it is
supposed to produce upon the
plasmic relation in the nucleus, as set forth by Richard Hertwig.
The more
new
Hydatena seem
recent researches of Funnett upon
Maupas and Nussbaum
(K. C. Funnett:
Hydatena, with some remarks on i»arthenogenesis.
7S
:
'22'6,
iy(.i6).
tliey lay:
;
;
and
(c)
the layers of
fertil-
A. Females giving rise to a high percentage
male producing individuals (arrenotokous females).
rise to a
pai'-
females, Funnett recognized from pedigree
first class of
cultures three different types.
be recognized
females which produce males
(h)
parthenogenetically (arrenotokous females)
of
may
females which produce females
(a)
thenogeneticalJy (thelytokous females)
Of the
Sex-determination in
Froc. Royal Soc, Series
In Hydatena three kinds of females
by the kinds of eggs
ized eggs.
throw
upon the subject in that they point out probable errors in the
light
studies of
B.,
to
B. Females giving
low percentage of male producing individuals.
C. Furely female
producing individuals (pure thelytokous females).
In experiments designed to test the effect of temperature and nutrition,
it
was found
that in the purely female producing individuals
(class C),
no male producing forms appeared, the strain remaining pure, and that in
the class B, the ratio of males
sequently
it is difficult
influence in determining
the
females,
really
producing
hermaphrodite,
was not
raised as a result of starving.
to see that either
male producing forms.
though
male gametes
the
orthodox form of spermatozoa.
Funnett suggests "that
parthenogenetically
females
we may
is
and
It
fertilization
may
exhibit
it
taices
are
the
ob-
nuist be supposed
place
be added also that
before
if
the
no polar
no reduction in the number of chi'omosomes, and
have, as has been clearly
shown
parthenogenesis but one of apogamy.
Determination of sex in Hydatena senta.
in a still
not
Such a view would account for the
accumulation of yolky material."
bodies are formed, there
(thelytokous),
may
served absence of polar bodies in the female eggs, for
that the process of reduction
Con-
temperature or nutrition has any
more recent study
of
Hydatena
in certain plants,
Whitney
Jrnl.
not a case of
(Whitney, David Day.
Exp.
Zool., 5: 1-26, 1907),
senta, finds that neither tempera-
44
He
ture uor iiutritiou lias aiiythiiig to do with the determiuatioii of sex.
asserts also that the three strains of Puuuett eau be found in one strain
and each
is
is
capable of producing the other types according as the data
scanty or extensive.
Even
if
we admit that
some evidence
the results obtained with certain animals furnish
favor of the view that nutrition
in
may
be instrumental in
determining sex, yef the vast majority of facts obtained from numerous
studies
made upon lower and higher
opposite conclusion.
shall
1
unmistakably
plants point
mention a few instances.
the
to
Botanists have long
recognized the difficulty of obtaiidng for class use the zygospores, or the
sexually formed reproductive bodies, in the
nigricans,
and
was supposed
this
to be
due
common bread mould Rhizopus
to the lack of
knowledge of the
external conditions necessary to call forth sexual reproduction.
has recently shown that this
common mould
is
dioecious,
Blakeslee
and that
male
if
strains are cultivated along with female strains, sexual reproduction will
take place ii:respective of external conditions
strains are
grown
food conditions
;
whereas
if
the different
separately, no zygospores will result, no matter
may
be
produces male and female sexual organs upon separate
thalli,
or individuals.
These individuals are propagated by bodies called gemmae, and
ported that Noll has cultivated individuals from the
sorts of
growth conditions without being able
the thalli.
alike,
The
what the
Again, the well-known liverwort, Marchantia,
thalli arise primarily
and that come from the same
be strictly male and others female.
to
is
re-
gemmae under
all
it
change the sex of any of
from spores that are apparently
capsule, yet
all
some of these spores must
The well-known
studies of Prantl upon
fern prothallia are frequently quoted as supporting the doctrine that food
conditions determine sex.
Prantl found that under poor conditions of nour-
ishment the prothallia produced only male organs, and
ditions
affording good
this as in
many
similar cases, there
organisms Avere operated with, that
male and female gametes.
opment
of the tissue
if
removed
to con-
nourishment, female organs were developed.
was no change
is
In
of sex since monoecious
organisms capable of producing both
Lack of nourishment merely inhibited the devel-
upon which the female organs are borne, and con-
sequently only male organs were developed.
These prothallia arise from
spores that contain the characters of both sexes, and external conditions
merely stimulate the development of one or the other of the sexes, or both.
The writer has
liave
recently begun the study upon a fern,
been reported as strictly dioecious, and that
if
whose prothallia
the spores are well
45
uourished female prothallia will predominate, while with poor uourish-
meut the vast majority
Au
of spores will give rise to male gametophytes.
examinatiou of cultures grown uuder favorable couditious for laboratory
use,
ill
which the spores were sown
produced
male
strictly
A
prothallia.
plants,
showed' that certain spores
thickly,
others
female,
and
still
others
bisexual
small number of spores were isolated and grown under
similar and very favorable conditions, with similar results.
were almost equal
in
number
to those bearing the
The pure males
female organs, while the
bisexual plants were few, being about four per cent, of the whole number.
The foregoing
results
mental conditions
seem
to lend
may have much
encouragement
less to
to the
view that environ-
do with the development of male
and female prothallia than had hitherto been supposed.
study showed clearly that in the fern in question there
among
the spores, which, as can
Among
the
mortality
first
The very
among
brief
a great mortality
be readily seen vary greatly in
things to establish in this and similar cases
greatest
is
is
the smaller or
larger spores,
is
size.
whether
and whether
the prothallia springing from the small spores tend to remain small and
produce only antheridia, while the larger female plants arise only from
the larger spores, an so on.
and extended study
Of
I
have no notion what sort of results a careful
will bring forth.
all efforts to
ascertain the influence of the environment upon the
determination of sex, doubtless the studies carried on upon dioecious plants
by Strasburger and
interesting
family, the
many
and instructive
Red Campion, Lychnis
Ustilago violaceae,
dioica,
is
dioecious,
staminate and others pistillate flowers.
pistillate flowers are
If
which
whose spores are produced
This red campion
pollen.
others are the most noteworthy.
Especially
in this connection is a representative of the pink
shown
is
attacked by a smut,
in the anthers instead of
certain individuals bearing only
The structure
of the staminate
and
in the following figure.
a plant, bearing staminate flowers, be infected by the smut, the
anthers
when mature
will be filled
with smut spores instead of pollen.
Apart from the color of the anthers the form of the staminate flower
unchanged by the presence of the parasite.
bearing pistillate flowers,
is
On
the other hand,
if
is
a plant,
befallen by the sniut^ the blossoms on the
branches affected by the .smut, will develop normally appearing stamens,
whose anthers are
remains
in a
filled
with smut spores instead of pollen, while the
rudimentary condition.
The only apparent
pistil
difference between
a pistillate flower thus affected by the i)arasite and the normal staminate
46
blossom
is ;ui I'loiiLjation
At
si,i,'!it
tirst
(•i(>nt
it
inl.L'ht
of the axis
botweon calyx and corolla
to chan.ne the sex of the plant, for the fnnsns,
pistillate
plant,
jiisril.
However,
in the
pistillate plant,
develop
and the
able to niduce the conditions necessary to their formation and
the suppression of the
own
snffi-
when present
in this case the capacity to
stamens must be assumed to be present in the
is
ob').
was
leads regularly to the development of stamens and the
snppression of the
parasite
(Fi.i,'.
ajipear that the presence ot the parasite
spores.
]^istil.
and thus provide
for the develoinnent of its
Extensi\e and elal)orate experiments
uninfected plants with
parasite, led to
no
tlie
bj'
Strasburger upon
view of duplicating the effects produced by the
definite results.
Fig.
3.
Fig. 3. Staminate aud pistillate Howers of Lychnis dioica L., halved longitudinally.
normal staminate Hower. b. normal pistillate Mower, a' staminate flower affected
by the smut, Ustilago violaceae; the anthers contain smut spores instead of pollen.
&' pistillate flower similarly affected: the pistil has remained rudimentary while anthers
have been developed, which, however, bear only smut spores. The presence of the
parasite has induced the development of anthers, the members of the flower bearing
male spores instead of the parts bearing the female spores,— After Strasburger.
a.
47
Laurent
favors
tlie
(1903)
lias
maintaiued that an excess of nitrogen or lime
development of males
in spinach,
hemp,
etc.,
while potash and
phosphoric acid favor the devo1o])ment of females, but his results are not
very convincing.
and vigor
pruning,
Temi)erature, light and moisture conditions, relative age
of parents, I'elative maturity of pollen, early
etc..
Iiave all been carefully
ing satisfactory or convincing results.
the foregoing seems to furnish
tlie
and
late planting,
and elaborately tested without achiev-
The case
best evidence
of the anther
among
smut
cited in
plants that the sex
of the spores to be developed can be changed by environmental conditions,
yet
must be admitted that the jjreponderance
it
of evidence is against the
view that environmental conditions, either direct or indirect, can determine
On
sex.
mined
is
the other hand, there are
in the
germ
<.'ells,
purely hereditary.
many who
believe that sex
is
predeter-
and that we are confronted with a probleui which
According to this view certain parts of the hereditary
substance or chromatin contain male characters, or repesent maleness only
and certain other parts female characters, or femaleness, that
is,
there are
male determinants and female determinants
in the chromatin.
To
illustrate
this statement, let us recall the case of the
common
liverwort, Marchantia.
Of the spores produced by any individual sporophyte, some will give rise
only to male thalli and others to female thalli irrespective of environmental
conditions. Now. the spores producing only male plants must contain only
male determinants, or male determining parts of the chromatin must dominate over the female determinating parts in those spores and vice versa.
If the
we
determination of sex be regarded as a problem of heredity, and
believe that hereditary jihonomena have a physical basis,
if
some such
theory as the foregoing certaiidy affords a rational basis for further investigation.