338 
PHYSIOLOGY. . 
BOOK II. 
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 
seemed finally established, never again to be seriously con- 
troverted ; for it must be admitted, that the denial of this 
fact, which has been since occasionally made by such men 
as Alston, Smellie, and Schelver, has carried no conviction 
with it. We know that the powder which is contained 
in the case of the anthers, and which is called pollen, must 
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 cir- 
cumstance, perfect plants. In cryptogamic plants, beginning 
with Ferns, and proceeding downwards to Fungi, there are 
either no sexual organs whatever, or they are not analogous 
in structure to those of flowering plants. 
In order to insure 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, 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 surrounding 
tissue is necessarily exhausted of its fluid, by the force of en- 
dosmose exercised by each particular grain of pollen. 
That this exhaustion of the circumambient tissue by the 
