106
DR. A. &RAP ON THE STRUCTURE
A short Exposition of the Structure of‘ the Ovule and Seed-coats
of Magnolia. By ASA GRAY,M.D., F.M.L.S., &c.
[Read Novexnher 19th, 1857.)
IN 1848, I maintained, in the ‘ Genera of North American Plants
Illustrated,’ vol. i., that the seeds of Magnolia were not arillate, but baccate, or in other words, that the fleshy coat was the
testa. In 1855 this view was criticised by my excellent and most
ingenious friend Mr. Miers before the Linnean Society (see Ann.
and Mag. Nat. Hist. for May 1855) ; and he, upon speculative
grounds rather than from immediate observations, concluded that
“ there is no reason to doubt that in Magnolia the scarlet envelope
is due to a subsequent growth over the primine,” and is therefore
an arillus. As soon as Mr. Miers’ remarks reached me, I reexamined the ovules and young seeds of the plants in question ;
and the results of new observations by Mr. Sprague and myself
were published in Hooker’s ‘ Journal of Botany,’ vol. vii. p. 243
(1855), and vol. viii. p. 26. The points which I supposed we had
settled by direct observation were :Ist, That no accessory covering, or arillus, was developed over
or upon the primine of the ovule ; but
2nd, That the fleshy envelope of the seed represents the priinine
or outer coat of the ovule ; and
3rd, That the bony coat of the seed was represented in the
ovule only by the innermost layer o f young cells, lining the primine ; which cells, multiplying by merismatic di$sion during the
growth of the seed, and their walls at length thickening and hardening irregularly, form the crustaceous or bony coat ; so that the
character of the seed is best expressed by the term “ drupaceous.”
Drs. Hooker and Thomson, about the same time (Flora Indica,
p. 73) also insist that the fleshy coat is the testa ; and notice the
delicate third coat, closely adherent to the albumen, but u-ithout
offering any opinion respecting the nature or origin of this and
the crustaceous coat *.
* Drs. Hooker and Thomson remark, that “the lateral position of the raphe
with respect to the ovule and seed is worthy of note. It is well represented by
Mr. Sprague in the plates of Asa Gray’s work just quoted, but is not noticed in
the text.” If this refers to the pericarpic position of the raphes, that is only
mentioned in the description of the ovules, although there is no need of it, as
that position is the normal one (wide Gem Ill. p. 10) j if it refer to the positioil
of the mphe on the middle of one of the broader aides of the seed, that is also
noticed in the deacription of the seed.
OF THE OVULE AND SEED-COATS OF MAGNOLIA.
107
Iam not aware of anymore recent direct investigation of the seeds
of Ma.9mlia. But in an elaborate memoir in the ‘ !Transactions
of the Linnean Society,’ vol. xxii., Mr. Miers argues the question
in detail, and reiterates his view formerly expressed, vie. “ that
the external 5eshy envelope must be arilliform, the thick osseous
nut must be the testa,” &c. j that the raphe, or’what he calls
the “ placentary sheath with its enclosed spiral vessels * * * afterwards becomes expanded by almost imperceptible degrees over
the primine, until it h a l l y envelopes it * * * and assumes the form
of a distinct scarlet fleshy covering over the testa, being quite
arilliform in its structure and appearance.” And my excellent
opponent goes on to state, that-‘‘ The only circumstmce that
bears any weight in the opposite view of the question, is one
which certainly ought to have its due importance, and is one
which I have never doubted in the smallest degree ; viz. that Dr.
Gray has watched the progress of the growth of the seed from
the ovule, and could never detect any subsequent or extraneous
production over the primine.”
This “ circumstance ” does not appear to have had much weight,
perhaps not so much as it was entitled to, considering that I had
declared that very easy observation in the living plant sufficed to
show that neither the fleshy nor the bony coat of the secd originated in the way Mr. Miers supposed, and had, moreover,
asserted that I had arrived, from direct Observations, at a different
explanation of their nature and origin. Although not disposed
to claim any particular authority for the observations made by
Mr. Sprague and myself, even while they remain completely
uncontradicted by any contrary observation, I may be allowed to
express the opinion that a very simple and bare statement of what
I said we saw, cannot properly be called an “ argument,” and still
less, “ ingenious reasoning.” And I might equally object to having
the candidly stated and unexpected discovery of the true origin of
the bony coat (the only thing of any consequence which we have
brought to light), described as an ingeniow substitution of an entirely new view of the subject, if I were not well assured that my
much-respected friend would, on reflection, at once disavow the
implication.
My present object is simply to publish a selection from the
sketches in which my observations (again repeated the present
season) have been recorded by the accurate pencil of Mr. Spwgue.
They tell their own story, and are naturally entitled to more
regard than my descriptive statement. I am indebted to the
108
DR. A. GRAY ON THE STRUCTURE
Smithsonian Institution for leave to make the present use of the
wood-cuts.
Fig. 1 represents a magniiled vertical section of a pistil
of Haygnolia umbrella, from a flower-bud about thirty
days before anthesis ; showing one of the forming ovules,
the other being cut away. The ovule at this time is an
apparently homogeneous cellular protuberance. Fig. 2
represents the ovule a week or two later in a similar
side-view : the two coats now appear as rings or shallow
and thickened cups around the base of the nucleus.
Fig. 3 is another ovule, as it appeared a few days later.
Fig. 4, another a few days later. Fig. 5, one from a Fig.1.
Q
I
Fig. a.
Fig. 3.
Fig. 4.
Fig. 5.
Fig. I.
fig. 6.
nearly full-grown flower-bud. Fig. 6, one from a justopened blossom. Fig. 7, a vertical section of the same
through the middle of the raphe. Fig. 8, a transverse
section of the same. In both these sections the conspicuous cord of vessels of the raphe is shown to occupy a F1g*8.
position about midway between the outer and h e r surface of
the primine, or external coat ; and this continues to be its POsition throughout the growth of the seed.
Fig. 9 is an outline section of a full-grown
ovule, like fig. 7, but on a larger scale, so that
the parts may be lettered and compared with
6a
the figures beneath : a, is the primine or outer
c
coat; b, the inner coat; c, the nucleus. Fig.
10 represents a slice of the tissue from the lefthand side of fig. 9, through the raphe and
primine combined, the inner coat and a little *J
Fig. 9.
of the nucleus; and fig. 11, a corresponding
~
c"
Fig. 10.
Fig. 1 1 .
slice from the right-hand side,-the parts lettered as in fig. 9, viz.
0, the outer coat ; b, the inner coat ; c, a portion of the tissue of
OF THE OVULE AND SEED-COATS OF MAQXOLIA.
109
th8 nucleus of an unimpregnated ovule. The cells forming the
h e r lining of the primine at this time hardly differ from the rest
except in their smaller size. Fig. 12 represents an impregnated ovule, or forming seed, of about a line and a half in
-a
length; its natural size is indicated by
a'
--6
the perpendicular line at the right of the d -figure. The raphe, turned toc
wards the eye, appears more
prominent than in nature, exI
cept when the body is a little
withered; it is then as conFig. 12.
Fig 13.
spicuous as is represented.
E g . 13 is a magdied vertical section of the same, answering to
that of fig. 9 : a, the primine, or outer seed-coat; a', its inner
lining assuming a different texture and appearance; b, the secundine or inner coat, already beginning to adhere slightly to the
nucleus c. On the other side, d is the cord of vessels of the
raphe. A slice of bhe tissue through d, and extending into the
a
nucleus, s d c i e n t d
a
'
b
C
ly magnified to reveal the structure,
is shown in fig. 14,
the parts of which
are correspondingFig. 14.
ly lettered. The
cord of spiral vessels, with some forming pleurenchyma, is still
found in about the middle of what becomes the fleshy coat of the
seed, while a stratum of narrow horizontal cells (a') are developing on its inner face.
Fig. 16.
Fig. 15.
Fig. 17.
Our nest stage eshibits the aeed almost full-grown, and of the
110
DR. A. QBAY ON MAQNOLIA.
size represented in fig. 15. This is taken early in July, about
three weeks before the cones begin to assume a rosy hue, and while
the crustaceous coat of the seed, although well developed, is only of
a firm fleshy texture, or just commencing to harden at the chalaza.
The tissue of the fleshy coat is by this time well fXed with scattered oil-receptacles. The raphe, visible externally when the
seed is a little withered, when fresh is hardly more to be discerned
than in a Paonia. Fig. 16 is an enlarged cross-section of fig. 15 ;
d, the cord of vessels of the raphe. Fig. 17, a longitudinal section ; a, the fleshy outer coat ; a', the forming bony coat ; b, the
delicate innel: coat, answering to the secundine of the ovule ; c, the
nucleus; d, the cord of vessels of the raphe. Fig. 18 is a seca'
a
d
b
c
Fig. 18.
tion of the tissue of fig. 17, and answering to fig. 14; the parts
correspondingly lettered. The only difference is that the aboutto-be bony portion of the testa is more definite and has much
increased in thickness. I n ripening, t h k soon hardens, and at
length its outer fleshy part turns red.
I f these illustrations do not make the matter clear, the objector
has only to examine the young seeds and ovules of Nagnolia for
himself. Although I do not perhaps completely understand how
Mr. Dfiers arrived at the conclusions which he still maintains, I
suspect it comes from his forming a wrong idea of the nature of
the raphe, and fiom mistaking for the raphe in Magnolia the
cord of vessels it contains. And I would ask him to make a comparative examination of the ovules and seeds of Pceonia ; which,
like many other anatropous seeds, at or before maturity, show 110
appearance of the raphe externally ; in which the cord of vessels
will be found more internal than in M i n o l k , and yet where the
fleshy surface of the seed will surely not be taken for an arillus,
while the homologue of the latter is plainly visible at the base of
the seed of most species. These seeds will also furnish convincing
evidence that two, or even three, strata of very different texture
may be developed from the primhe or outer coat of the ovule.