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that time it seems that they must have undergone many crosses. I believe that our
commercial canes are of the weaker rather than the stronger forms from these islands.
If we look at the Philippine Islands, we observe that they have their own canes
which I believe were brought back from such' i~hnds as New Guinea or the other
islands of Melanesia. The importance of sugar cane in this region' is very interest'
ing and significant. Sugar cape is both meat and drink for the primitive men ,woh
dwell there.
Dr, .Brandes: I have followed these comments with a good deal of interest as
they appear 'to reveal that Dr. jeswiet has given his attention to the problem of the
origin of cultivated canes. My own interest is more narrow, being confined to the
possible production of disease resisting kinds but it is evident that we must be at
least partly on common ground.
Mr. Moir: We have in Hawaii about fifty varieties of New Guinea canes that
were evidently brought to the Island by!~the early Polynesian navigators. They can
be identified as New Guinea canes by comparison with more recent introductions.
Some of those at a certain age show mosaic and at a later time the mosaic disappears so that. it is practically impossible to find symptoms but we got mosaiced plants
from the portions of the stalk infected. Dr. Brandes, I believe, knows this collection.
March 19, 1927. 2 P. M.
Mr.
J.
R. Johnson in the chair.
Dr. Brandes: In resuming the discussion of mosaic diseases it has perhaps only
a scientific' interest but I would like to take up for a few minutes a matter in which
I have had a personal interest for many years; that .is, the etiology of mosaic and
certain biological phenomena in connection with infection. I have· brought to the
meetings a number of interesting slides showing the actual inoculation of sugar cane
and other plants including corn, teosinte, sorghum, Syntherisma sanguinalis and
Chaetochloa magna by means of the insect vector, Aphis maidis. These slides are
from phatomicrographs of serial sections of the leaf and the insect at the moment of
feeding. This is a matter upon which I have already published but we have now
an abundance of additional evidence confirming the soundness of the conclusions
previously advanced, namely, that the excretion that pours from the tip of the setae
bundle as it advances' through and between the leaf cells is the actual medium by
which the virus is introduced into the plant It is further found that the phloem
tissue of the vascular bundles is invariably sought by the insect for food. You will
note in all of the slides the dark colored excretion or saliva which stains a deep red
with safranin. (Slides indicating the penetration of the setae bundles into the plant
tissues are shown). It penetrates to the sieve tubes and companion cells in every
case. The insect is secking food and it would appear logical that the phloem, richer
in liquid nutrients than the other leaf cells, should be attractive. It is possible also
that the mosaic organism, it is such, finds a favorable medium in the elaborated food
which is transported from the leaves' to the storage tissues by means of the phloem.
At any rate the evidence seems to point out that the virus, once it enters the phloem
of the vascular' bundles, is rapidly translocated to all parts of the plant through the
tissue. It may also later permeate other tissues and the pathological changes that
have been observed in the parenchymatous cells, rich in chloroplastids, support this
hypothesis. It must be borne in mind, however, that such pathological changes need
not necessarily depend upon the actual presence of the organism in those cells. In
109
other words, it might be an indirect effect in which. a deranged physiological activity
of one group of cells causes pathological changes in another group dependent upon
the first. In support. of the idea that the phloem is the tissue by which the virus
is actively transported, we have, the recent observations of Mr. C. W. Bennett of
the Michigan State College on a raspberry mosaic. Bennett found that by girdling
a raspberry cane, and thus destroying the cambium layer at that' point, he could
prevent the advaace of the disease past the injured portion. To select a typical
experiment a colony of viruliferous aphids were placed on the terminal leaf of a
raspberry cane after the cane had been girdled several feet from the tip. Theleaves
gradually developed signs of mosaic beginning with the tip leaf on which the aphids
were colonized and involving successively the leaves in the downward direction but
the advance was abruptly stopped at the point where girdling had taken place. All
leaves below the part that had been girdled remained healthy during the experiment.
The same phenomenon was observed when the inoculated part was below the point
of the girdle. The leaves from that point out to the tip remained, to all appearance,
healthy. Admittedly this is not conclusive but it supports my view that the phloem
of the vascular system is the means by which mosaic virus rapidly spreads.
Another interesting phenomenon which you will note in one of the slides, and
which was observed by Mrs.R. C. Starret who was associated with me in this work,
is the decided stimulation of the nuclei in cells lying along the path of the, setae
puncture. The cells rapidly migrate until they all lie adjacent to the setae. bundle
or as close to it as possible. This is an interesting evidence of response to an irritation. It may be merely for regenerative purposes as the delicate cells are doubtless
injured by the passage between them of the minute setae bundle lubricated, as above
described, by the excretion which exudes from its tip.
Mr. Matz: I should like to mention that we do see destruction of tissues out,
side of the vascular bundles. I am inclined to believe from my studies that there
is a destruction of cells in the stalk' and in the chloroplasts of the leaves and that
this is a direct effect' of the virus. I believe others also have tried to find if there
is a material change in the. size of the chloroplasts. In my cytological studies I
found infected .leaves always show a marked reduction in the' size of the chloroplasts.
The destruction of paranchyma ecells of the cane cannot be attributed to anything
other than the direct effect of the mosaic virus.
Dr. Brandes: We have no definite proof that the virus is confined to the phloem
and in' fact it is logical to suppose that eventually it permeates' other tissues but I
believe that the phloem isa tissue to which the insect directs the virus. Reduction
in the chloroplasts could be' accounted for by indirect action of the virus, but my
observations and Bennett's, is that the phloem cells of the vascular bundles are par'
ticularlysoughtby the setae of the insect and that probably this tissue is the means
of translocation of the virus throughout the plant at a fairly rapid rate. The evidence
points out that it is not 50 translocated by the xylem.
Mr. Mati: There is no other factor to which we coult attribute the dead cells
outside' of the presence in the cane of mosaic virus. By more careful or more as'
siduouswork we might be able to find an .organism in the dead cells tissues in which
the effects of the disease are very evidently localized.
Mr. Johnston: Would you not consider it self-evident that the virus on being
absorbed is going to pass out to other tissU~S?kJ'
110
.' :~;;
Dr. Storey: Dr. Brandes, do you consider the rate of ~ad;~riGe of the virus as
found in the curly top of the sugar beet, namely, six inche;;iQ:~n:e hour, consistent
with the rate of transfer of the mosaic virus through the phloem?
Dr. Brandes: There is so much difference of opinion among plant physiologists
concerning the rate of translocation of soluble substances in the phloem tissues that
it cannot be said with certainty whether our theory is consistent with them.
Mr. Matz: After many examinations .of the different elements in the fibrevascular bundles of mosaic cane, including the phloem cells, no apparent abnormality
was found in any of them, yet we do find irregularities in the cells. outside of these
fibrovascular bundles.
Mr. Johnston: I do not see that we need to conclude that the virus must necessarily invade all affected cells since, if the toxin is readily absorbed, it may pass
through to the other cells. Since the time is growing short, let us proceed to a discussion of leaf spots and I will call on Dr. Fads who has prepared a' report on this
subject for Cuba.
SOME SUGAR CANE LEAF SPOTS IN CUBA
By James A. Faris
(Eye Spot Disease, Brown Stripe, Ring Spot, Leaf Blotch, Spindle Blotch
and Cold Chlorosis).
This paper presented by Dr. Faris, suggesting Brown Stripe and Spindle Blotch its
two sugar Ca-ne diseases hew to science, was publisheh in Facts About Sugar
for December 3 1927.
DISCUSSION OF SUGAR CANE LEAF SPOTS
Mr. Rosenfeld: I noted cold chlorosis in cane in Peru where it is called "frio"
locally. Furthermore, I wish to say that D 433 cane has been observed to be
particularly susceptible to Helminthosporium spot in Porto Rico.
Dr. Brandes: The chlorosis caused. by low temperature is well known in-Louisiana where the Type mentioned by Dr. Faris is known as banded chlorosis. I have
observed exactly the same thing in greenhouses in Washington during the summer
time when the temperature is very high and have attributed it to the effect of water
accumulating in the lower part of the leaf whorl following syringing. The heat sometimes becomes injurious to the juvenile tissues of the spindle and when the spindle
finally unrolls, every leaf will be marked by a banded chlorotic area.
.
Dr. Jeswiet: This condition has been noted in Java also arid I think it may be
caused by' high temperature and by drought as well. The tendency is to retard
growth and .that retarded part, when it emerges, is white.
.
Dr. Faris: Probably either extreme of. temperature will cause suppression of
chlorophyl development.
Mr. Crawley: It may be interesting to call attention to the fact that I have
observed whole fields of Kavangire cane with· these white bands' at Central Maria
Luisa.
Mr. Rosenfeld: There is another chlorotic condition in this same Kavangire in
Porto Rico characterized by longitudinal striping of the leaves.
.