REPRODUCTION IN LOWER PLANT LIFE. 109 
Let us now endeavour to draw some general conclusions 
from the array of facts I have endeavoured to present to 
you. It is usual, in works on Physiological Botany, to 
distinguish between two kinds of multiplication in the 
vegetable kingdom,—reproduction and propagation ; under- 
standing by the former the production of an entirely new 
individual by a sexual process, by the latter the continu- 
ance, by a process of special vital activity, of some 
particular portion of the old individual. This distinction 
is a very useful one in practice; but we must be careful 
not to push it too far. In Classification we have long 
learnt that Nature refuses to be mapped out into squares 
like a chess-board, and that in any natural system of 
taxonomy the various classes and divisions must slide into 
one another by insensible gradations. So in Morphology 
and Physiology. It is all very well to say :—This organ 
is constructed in such or such a manner, and is fitted 
for such or such a purpose; while another organ has a 
totally different structure and a totally different purpose. 
No doubt it is so where differentiation has made great pro- 
eress. But just as, in the lowest types of life, we find 
archaic forms from which the most complicated might 
have been derived, so also we find rudimentary structures 
with many functions, or even capable of taking up, accord- 
ing to circumstances, totally different characters. Plas- 
ticity 1s the great feature of a low type of life. We have 
seen, in such familes as the Confervacee, an apparent 
identity in structure between the male and female 
~ elements. And, what is more instructive still, we find, 
in a considerable number of families of green Alow, that 
the zoogametes which do not conjugate, whether male or 
female, are capable of germinating into new individuals ; 
though, as far as observation has gone, the new individuals 
thus produced are always weakly, and generally soon perish. 
