CHAP. VI. 
FERTILISATION. 
281 
trace the progress of discovery of the precise nature of the 
several parts of the stamens and pistil. Suffice it to say that, 
in the hands of Linnaeus, the doctrine of the sexuality of plants 
was finally established, never again to be seriously contro- 
verted; for the denial of this fact, which has been since 
occasionally made by a few men, such as Alston, Smellie, and 
Schelver, has merely exposed the weakness of such hyper- 
critics. We know that the powder which is contained in the 
case of the anthers, and which is called pollen, must generally 
come in contact with the viscid surface of the stigma, or no 
fecundation can take place. It is possible, indeed, without 
this happening, that the fruit may increase in size, and that 
the seminal integuments may even be greatly developed ; the 
elements of all these parts existing before the action of the 
pollen can take effect: but, under such circumstances, what- 
ever may be the developement of either the pericarp or the 
seeds, no embryo can be formed. This universality of sexes 
in vegetables, must not, however, be supposed to extend further 
than what are usually called, chiefly from that circumstance, 
perfect plants. In cryptogamic plants, beginning with ferns, 
and proceeding downwards to fungi, there are either no 
sexual organs whatever, or the males are so imperfectly deve- 
loped as to be invisible, or of no effect. 
In order to ensure the certain emission of the pollen at the 
precise period when it is required, a beautiful contrivance has 
been prepared. Purkinge has demonstrated the correctness of 
Mirbel's opinion in 1808, that the cause of the dehiscence 
of the anther is its lining, consisting of cellular tissue, cut into 
slits, and eminently hygrometrical. He shows that this lining 
is composed of cellular tissue, chiefly of the fibrous kind, 
which forms an infinite multitude of little springs, that, when 
dry, contract and pull back the valves of the anthers, by a 
powerful accumulation of forces, which are individually 
scarcely appreciable : so that the opening of the anther is not 
a mere act of chance, but the admirably contrived result 
of the maturity of the pollen, — an epoch at which the sur- 
rounding tissue is necessarily exhausted of its fluid by the 
force of endosmose exercised by each particular grain of pollen. 
That this exhaustion of the circumambient tissue by the 
