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100 ON THE SEXUAL ORGANS OF THE CYCADACE.i;.
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 diifer 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 characteristics 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 macrosjiores belong-
ing to the same species, but to different individuals. The dimorphism
and triniorphism of flowers, digamic fertilization,—originally pointed
out by Sprengel, in his admirable work (' Das entdeckte Geheimniss
der Natur,' etc.), 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 sclf-fertiliziition 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 Avhich 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 dioecious and moucecious gTOups, and generally among
plants which are not self-fertilizing. The ascent of organization to a
higher grade of complication 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 iu
the conditions of the fertilized embryonal vesicle.
* Fr. 'Hildebrand, ' Die Gfeschlechtsvertheilung bei den Pflanzon,' 1867.
f Among wholly inexplicable phenomena, we must incontestably include the
law that many hermaphrodite ilowers cannot fertilize themselves, and that
they need the intervention of another flower of the same, or even, in some
cases, of a different 8i)ecies. " Nature tells us, in the most emphatic matter,
that she abhors perpetual self-fertilization" (Darwin). Has there been in the
f