100 ON THE SEXUAL ORGANS OF THE CYCADACE.X. 
new being, are not in every respect and in every case in a uniform re- 
lation. If we measure the fertile pollen grains of any one species, we 
find them, it is true, to have an average size, but they may differ one 
from the other in dimensions, not to speak of difference in contents. 
It is the same with the parts of the female organ. The fertilized 
embryonal vesicles ought equally, therefore, to differ from one another 
in the same individuals. They combine the characteristics both of the 
male and female parent, as is shown in a striking manner by the pro- 
duction of hybrids, but these characteristies are combined, in each 
case, in a slightly varied relation. This law, the effects of which are 
so decided in hybridizing, ought also to make itself felt, although in a 
less degree in the conjunction of microspores and macrospores belong- 
ing to the same species, but to different individuals. The dimorphism 
aud trimorphism of flowers, digamic fertilization, —originally pointed 
out by Sprengel, in his admirable work (‘ Das entdeckte Geheimniss 
der Natur,’ ete.), and which Darwin and many other writers in the same 
direction have placed in a more striking light, —must convince us that 
even among hermaphrodite plants, the self-fertilization of flowers is 
much more rare than had previously been believed.* 
The change of form of the species is thus involved in fertilization ; 
and in the succession of individuals, over which this function presides, 
we establish the law, that in each case the last generation must differ 
a little from that which precedes it. Ought we not to attribute to this 
intrinsic principle of variation, in addition to the action of natural selec- 
tion, and of external conditions, a considerable influence in the progres- 
sive development of the vegetable kingdom ? If such is really the case, 
the maximum of modification, the greatest variety of forms should be 
met with in the dicecious and monecious groups, and generally among 
plants which are not self-fertilizing. The ascent of organization to a 
higher grade of complieation is a law written in the history of the 
organic world, and the true cause of which resides in organization itself, 
just as the development of the individual is invariably determined in 
the conditions of the fertilized embryonal vesicle.t 
r. Hildebrand, ‘Die | eae ee ie. De bei den Pflanzen,’ 1867. 
law that many hermaphro: dioi lowers x n “fertilize themselves, and tha 
-E need zin ———— of another flower of the same, or even, in some 
pecies. ** Nature tells us, in ced most emphatie ai 
ect she ene dier Scl fertilization ” (Darwin ) Has there Seen in 
