OF TRIGIDIA. 23 
retained a somewhat concave form, but the small cells 
are overlapping, and present no symptom of violence 
(fig. 9, a, 6). 
On the third day after the impregnation of the ovule, the 
granular contents of the impregnated embryo-sac have col- 
lected together in a more or less elongated form, the anterior 
extremity being in contact with the imner surface of that 
spot of the embryo-sac where the contact with the pollen- 
tube occurred. The anterior end receives a sort of concave 
edge from the still existing depression in the anterior part of 
the embryo-sac. Ten days elapse, and the ovules, greatly 
increased in size, have a tough external coat, and the embryo- 
sac is very remote from the micropyle ; the presence of cells 
is now evident within the sac, whose simple overlapping cells 
are becoming thick and hard. 
V.—There is no difficulty in the manipulation necessary 
for these investigations ; the ordinary flat knives and needles 
will suffice as instruments, and water, glycerine, and the 
usual reagents, are necessary. The impregnation of the ovule 
differs as regards the time it occupies in most species ; more- 
over, temperature and moisture determine its rapidity. The 
stigmas of some plants are impregnated before the flower is 
perfectly open; others remain virgin for a long period. It 
will then happen that, unless the nature of the efflorescence, 
the duration of the flower, and the time of the increase of the 
diameter of the style be noticed, the microscopist may look 
in vain for any trace of pollen-tubes. The rapidity with 
which some ovules in plants with very short styles are im- 
pregnated can be well imagined after what has been brought 
forward in reference to the rate of pollen growth in Tigridia. 
Immediately after the impregnation, changes commence in 
the pollen-tube, as well as in the whole of the female organs. 
The tubes become flaccid, all granular movement ceases, and 
they lose their tenseness. The style is swollen by the de- 
scent, through cell-growth, of the numerous pollen-tubes ; 
the nutrition of its central cell system is at its height, and 
this vital activity is kept up until the tubes pass into the axis 
of the ovary. Then the stigma and upper part of the style 
droop, and the perianth begins to lose its brightness, to be- 
come flabby, and to fold. The ovules are not yet impreg- 
nated. After a few hours the pollen-tubes passing down the 
axis, nourished by its juices, are turned off laterally by the 
barriers formed by tough vascular tissue which passes off to 
each ovule; the tubes pass through the papillary structure 
near the placenta, and reach the micropyle. The nutritive 
