FRESH-WATER ALG. 199 
spore? By what power is a plant given to under- 
stand, that a similar plant lies in its immediate 
neighbourhood, ready to carry on the necessary 
fructifying process? Certainly we can consider it 
nothing else than a species of the same indefinable 
operation, which prompts the bee to construct a 
cell of an hexagonal form, or a bird to build a nest 
in the manner peculiar to its species. 
We thus find that these obscure plants form no 
exception to the very general, if not universal law 
that each species of living being requires two dis- 
tinct elements for its perpetuation. Sexual ele- 
ments have been detected in most of the crypto- 
gamic plants, and in a short time will probably be 
discovered in all. The power of reproduction by 
segmentation, or the production of numerous suc- 
cessions of asexual fertile generations, which, in 
common with many others of the humblest organ- 
isms, vegetable and animal, the conferve possess, 
is in all cases limited, the species necessarily re- 
verting to sexual admixture for its perpetuation. 
The germs produced by the conjugation of ap- 
proximated individuals, when fully ripe, burst the 
cells in which they are confined, and are consigned 
to the surrounding water, where they float about, 
until they meet with some substance to which their 
mucilage enables them to adhere; and once esta- 
blished in a congenial situation, they spring up into 
