346 
POPTJLAE SCIENCE EEVIEW. 
are often barren, while the later ones, which have no corolla, are 
fertile. Von Mohl has seen the pollen escape from the anthers 
on to the stigmas and give out abundance of pollen-tubes. 
Monnier says that the ordinary spring flowers of Viola hirta 
and odorata never produce seed ; but this statement is disputed 
by others. The “cleistogamons” flowers of the violet appear long 
after those that are so familiar in the spring, and may be found in 
abundance about July and August, very small, but still not difii- 
culttomake out. Fig. 7, a, shows the appearance of one of these 
unopened flowers, the only visible part being the five sepals, of 
nearly the same form, though much smaller, than the ordinary 
ones. On opening the appearance is presented shown in 6 ; no 
trace of petals ; there are five stamens, two of them repre- 
sented in the figure, with long filaments and very small anthers, 
offering scarcely any resemblance to those of the open flowers, 
which have very large anthers and no filaments. The pollen, 
again very small in quantity, is contained in two almost trans- 
parent bags at the base of the anther, shown at n in c, and is 
discharged directly on to the stigma. The pistil, d, consists of 
a conical ovary, and a very large stigma curved completely over 
in a semi-circle so as to bring the papillose receptive surface 
{st) into a horizontal position in which it will most readily receive 
the pollen. A most instructive contrast is afforded between 
the arrangements of the reproductive organs in these two kinds 
of flowers on the same plant. In the showy spring flowers the 
stigma projects horizontally in the form of a beak above and 
quite clear of the stamens, the arrangement of which is such 
that it is scarcely possible for any of the pollen to reach the 
stigma without the intervention of insect agency. In these 
closed summer flowers it will be seen that the arrangements 
have evidently an exactly opposite purpose. They produce 
abundance of seed. Another section of the genus Viola, of which 
the wild pansy ( Viola tricolor) may be taken as the type, produce 
no cleistogamous flowers ; and the contrivances for fertilisation 
are, as has already been mentioned, quite difl*erent from those 
in the true violets. 
In two Indian species of Campanula, the closed flowers are 
described by Professor Oliver as being altogether different in 
shape to the conspicuous ones. They are covered by a com- 
pletely closed membrane, the rudiment of the corolla ; the 
stamens are extended horizontally, and the anthers are quite 
connate, and together adnate to the stigma. As the flowers 
have only at present been observed in dried herbarium speci- 
mens, the mode in which the pollen-grains reach the stigma is 
still uncertain. In Juncus hufonius it is said that the pollen- 
tubes are emitted while still within the anther, the wall of 
which they pierce. In the wood-sorrel, Oxalis acetosella^ the 
