•J8 THE FEJÌTILI2ATIO:Ì
Results of cìiltlKciUons of the pollen of Ficus MoxbtirgJiii.
A very exteusive series of cultivations was carded out, both on the stigraatie
surfaces of receptacles ready for insect access, and in suitable fiuid media in sealed
Tvax-cells. In the case of the cultivations ot the first kind, the receptacles were
divided transversely, pollen from mature anthers was smeared over the stigmatic
surface o£ the lower half, the upper half was again fitted on and pressed into close
contact, and the receptacle was then placed in a moist chamber. In the other class
of cultivations, pollen-grains were immersed in a drop of fluid suspended on the
under surface of the coTCr-glass sealing a wax-cell. The solution which gave the
best results was a one per cent, one of cane sugar in water, and with this much
more constant and extensive evolution of pollen-tubes occurred than in any cultivations
o n the stigmatic surface. One great objection to the latter was found to lie in the
f r e q u e n c y with which growths of fungal mycelium made their appearance, the filaments
h a v i n g a very marked tendency to adhere to the pollen-gr-ains, and in many cases actually
p e n e t r a t i n g and pa.ssing through them from one end to the other, so that they came
t o be strung like beads on a thread. Tliose grains which cscaped in many cases germinated,
e m i t t i n g one or two tubes, but the growth always remained very limited. The tubes
were very short, and had a great tendency to become dilated at their extremities, after
which no further growth occun-ed (Plate IV, figs. 11, 13). In the case of the coverglass
cultivations there was not so much liability to fungal intrusion, and the tubes grew
much more freely. Here tliey often attained a considerable length, the protoplasm grad
o a l l y travelling outwards, and frequently leaving the grain at a considerable distance
b e h i n d as a mero empty shell. Ultimately, as in the stigmatic cultivations, a distal
d i l a t a t i o n made its appearance, in which the protoplasm accumulated and from which it was
finally discharged into tliG surrounding fluid (Plate IV, fig'. 13), In .souie ciises in stifniatic
cultivations, and more frequently in cover-glass ones, a few tubes showed a tendency to
branch, but the resul t ing twigs always remained very short (I'late IV, fig. 13}.
Ifotes on the life-history of the flrj-inseet affecting Ficus Itoxlmrghii
in Calcutta.
I n the above heading the words "in Calcutta" have been deliberately introduced,
because it remains uncertain whether the insect which is here related to the species is the
same as that related to it in its normal habitat, and specific to it, or whether we have not
to deal with a case of appropriation of an exotic host by an insect properly related to one
of the figs native to the locality. There are some grounds for suspecting that this really
I n the first place, it is somewhat hard to imagine how the insects,i s t h e c if spe c i f i c a l ly
r e l a t e d to the tree, were originally introduced to Calcutta. They certainly could not have
been normally introduced by the plants first imported, as these were not at a stage to
produce any fruit. It is, of course, possible that they ma y have been imported in receptacles
of F. Ratslurghii, or accidentally along with other materials sent down to the Botanic Garden
i n Calcutta f rom the native habitat of the t ree; but, as the life of the female insect appears
to be very brief after emergence, end as the latter only occurs in detached receptacles when
t h e y have been plucked when qnite mature, and then very rapidly, there are difficulties
i n the way of accepting this as a probable event. On the other hand, there are certain
OP FICUS EOSBUEGHir.
phenomena which, at all events, appear to favour the hypothesis of appropriation by
insocts native to the new locaUty. Tor example, daring the month of October 1888
specimens of both gall and female receptacles were obtained in the Botanic Garden
which had been quite recently entered by insects of the normal species, whilst, in so
f a r as could he ascertained, no mature gall-receptacles had been formed tor a 'period
of months on any of the trees there or in the Zoological Garden at Alipore. It appears
then, quite possible that the insect is not specifically related to the tree, but that it is
either normally common to it and some other species, or properly holengs to another
species, and has appropriated this on importation. Without specimens of the insect
n o r m a l l y related to the tree in its native habitat and a complete set of all those affecting
t h e species of figs occurring about Calcutta, neither of which have yet been obtained it is
impossible to come to a definite conclusion on the point, and it is merely alluded
t o here as one calling for further enquiry.*
Whether, however, the insect be native or exotic, specific to R Rozlur,M or common
to It and other species, there is no doubt that it is a single species which affects
t h e trees m Calcutta, and is essential to the production of mature pollen and of fertile
seods there, and that this is, as I am informed by !Hr. Wood-Mason, a species of
J i t f m i « . In dealing with its life-history it is convenient to take as a starting point
t h e period when a largo gall-receptacle to which individuals belonging to a previous genera
t i o n of fertilized females have gained access is attaining the final stages of maturation
1 he fii-st certain index to the occurrence of these is a softening of the walls of tlm
receptacle, and a diminution in their tension connected with diminution in the supply
of sap reaching them and absorption of the receptacular fluid. The walls now give perc
e p t i b l y on pressure and, at the same time, their colour has changed from green to a
reddish-yellow. If such a receptacle he laid open, the interior of the cavity is found
merely moist, with a veiy thick stratum of the enlarged ovaries of the gall-flowers
u n i f o r m l y covering the surface, save over the centre of the ostiolar face, where a
g r e a t mass of closely-packed filaments and anthers forms a conspicuous prominence The
surface is everywiiere, save over tho staminal prominence, stained of varying shades
of madder-brown, due to deposit from the absorbed receptacular fluid; the depth of tint
of various areas being, as previously mentioned, apparently related to the position ot
t h e receptacle favouring excessive deposit ia some places. Sometimes, too, patches or
fine webs of fungal mycelium are recognisable on some parts of the surface Tile
solid mass of closely appressed ostiolar bracts bfiieath the mass of over-archino- male
flowers IS of very considerable thickness, even in relatively small receptacles attaining
a thickness of neai- O o". ^
I t is only for a brief period that the mature receptacle« retain the above characters for
t h e insects b egm to emerge within a short time. For some time in normal cases mal e inLcts
alone make their appearance, gnawing their way out of the ovaries and crawlinc awkw
a r d l y about over the surface to perforate the flowers containing the females and to impreg
iiato the inmates. They are amber-coloured, wingless, and wi t h ver y strong jaws and telescopic
abdomens. Gradually more and more of them converge to the central area ot the ostiolar
face of the cavity and commence to at tack the male flowers. With their powerful jaws they
c r i through filaments and anthers iudiscmiaatcly, and soon reduce the mass of male flowers