4.6 ON THE FEETILIZATION
o n l y that a single insect can conrey many thousands of pollen-grains with it in
spite of the excessive obstmctions to access presented by the ostiolar plug, but that
these grains are also most methodically and economically distributed, for, unless each
stigma were only allowed to appropriate a single grain, the amount introduced would
haye to be indefinitely multiplied.
T h e occurrence of ordinary pollination thus appears to b e impossible, and the only
way in which a sufficient number of pollen-tubcs could be reasonably supposed to orig
i n a t e would be by means of peculiarities in their derelopment, the primary tubes
o r i g i n a t i n g from the grains having a capacity for indefinite gi-owth and ramification,
so as to give rise to mycelioid expansions from which branches might be distributed
t o the individual stigmata. There is, however, no evidence of the actual occurrence
of any such phenomenon. There is nothing to show that the tubes, whether developed
within the receptacular cavities or as the result of artificial cultivations in
suitable media, have any special tendency to branch, far less that they have any capac
i t y for indefinite mycelioid extension.
T h e most important evidence against the occurrence of pollination of any sort as a
normal and essential event lies, however, in the fact that the embryo originates, as it does
i n undoubted cases of development, apart from pollination. The embryo, as a rule for
of course it is possible that pollination and normal evolution may occur in certain individual
flowers—certainly arises as an outgrowth of the nucellar parenchyma outside the
embryo-sac, and not as the result of special evolution of any elements contained within
t h e latter The embiyo-sac up to the period of insect-access and of initial development
of the embryo normally retains the characters of a simple, uninucleate cell. There is
n o evidence of the formation of an oosphere, of synergidaj, or of antipodal cells within
it, and it is only subsequent to commencing evolution of the embryo that the primary
nucleus is replaced by a lai-ge number of secondary ones which are apparently related
t o the elaboration of food material for the growing embryo when it gains access to
t h e cavity of the sac.
But if this be so, if pollination be unnecessary, why should the access of insects be
essential to the development of embiyos? The phenomena presenting themselves in
connection with the male flowers of gall-rGceptacles appear to afford a clue to answerinot
h i s question. It is just as impossible for the male flowers to come to perfection—juse
a s impossible for perfect pollen-grains to be developed witliout the access of insects to
t h e gall-receptacles—as it is for embryos to be developed in female ones under parallel
circumstances. In the case of the male flowers, however, it is clear that the introduction
of pollen int o the receptacular cavity cannot be the essential determinant of development,
but that this must be related to something else connected with the access of the insects.
I t is not anything directly introduced by the insects that determines the perfect evolution
of the male flowers, but it is due to effects which their entrance produces on the recept
a c l e that the evolution becomes possible. The result of the access of the insects, of their
p u n c t u r e of the gall-flowers and deposition of ova in the interior of the nucelli, is the
induction of great irritative stimulation to the activities of all the tissues of the receptacle.
T h e entire mass of the receptacular tissues undergoes hypertrophic changes similar to
those occurring in the development of any common gall-growth, and connected with their
occurrence an enormously increased flow of sap to the receptacle takes place, as indicated
b y the accumulation of fluid under high pressure within the receptacular cavity, and
t h e abundant escape of latex on division of the peduncle or incision of the surface.
0 ? FICUS ROSBURGHir. 4 7
T h e maturation of the male flowers is, then, clearly a result of general irritativa
h y p e r t r o p h y of the receptacular tissue as a whole, due to insect access, and not the
result of the addition of any extraneous bodies to them ; and when the rest of the
evidence is taken into account, there can be little doubt that the phenomena presenting
themselves in connection with the true female flowers are of essentially similar nature
and origin.
I t may be objected that in the case o£ the female receptacles no deposit of ova
within the tissues takes place, and that, therefore, a source of irritati\'e stimulation of
suflicient magnitude is wanting. But although no ova are successfully deposited within
t h e ovaries of the true female flowers, owing to the strength and thickness of their walls,
t h i s by no means implies that attempts at deposit are not made. On the contraiy, as
has already been pointed out, the insects which attain access to female receptacles go
o n perseveringly attempting deposition until they are worn out and die ; or, in other
words, they go on perseveringly stinging the ovarian tissues as long as their life lasts.
But it is the process of perforation, which is probably the real determinant of hypertrophy
i n the gall-receptacles, and not the mere deposition of the ova, which profit by its
presence. The essential stimulus is thus alike in both cases ; and this being so, parallel
results naturally follow, and maturation of pollen-grains in the male flowers and embryogenie
growth of a specialised portion of the nucellar tissue in the female ones take
While this is so ; while the development of embryos as a rule occurs independently
of pollination, it is of course possible that exceptions may occur, and that the embryogeny
of certain flowers may take place in the normal fashion; and it is even possible that the
embiyos arising in this way may have a stronger vitality, and therefore more chance
of ultimate survival, than the others: but if this be the case, it can only be so as an
exceptional phenomenon, for among the hundreds of ovules which I have examined I
have never seen anything suggestive of its occurrence.
T h e development of embryos in F. ]ioxhurghii, then, appears normally to be an
asexual process dependent oq hypertrophic budding of a specialised portion of the nucellar
parenchyma, and it appears not improbable that the phenomenon is not peculiar to the
species, but is the rule in the case of other figs also. This, of course, requires further
i n v e s t i g a t i o n ; but in the only instance in wliich I have yet had time to examine the
m a t t e r — i n the case of F. Jdspida—iXxQvB can be no doubt that it is so.
I n conclusion, I have to express my obligations to my friends Dr. George King
a n d Dr. Gerald Bomford: to the former for having first directed my attention to, and
supplied me with materials for the investigation of the subject dealt with in the previous
pages, and to the latter for a very fine set of serial sections of ovules from receptacles
before and after insect access.
D. D. CUNNINGHAir.
^^ovP!}¡l>er 1888.