Evolution in the Plant Kingdom. 333: 
as the highest expression of differentiation in the seventh and last. 
Although vegetative organs have departed from the sex-phase, 
there still remains a double function, namely, the production of 
male and female cells or organs. It seems to bea law, that so long 
as anything remains to be differentiated, differentiation will con- 
tinue; and the separation of the sex-organs is its next possible: 
expression. Instead, therefore, of having .a single prothallium 
bearing both male and female organs, we find two prothallia ; one 
male and the other female. This state of things is reached by one 
set of organs first becoming functionless, and finally being sup- - 
pressed. Remembering that these prothallia are developed from 
asexual spores, it does not seem strange that this dicecism extends 
presently to these spores themselves, and that we soon find what 
may be styled (from the nature of their product) male and female 
asexual spores. This brings us to the heterosporous arrangement, 
a feature which continues to the last, and which must be considered 
a high-rank character, possessed only by the higher members of 
the sixth group, and by the seventh; and yet, through the very 
midst of this condition of things, accompanied as it is by many 
intergrading characters in all the other plant structures, the old 
abyss between Cryptogams and Phanerogams was supposed to 
run. To sum up the lines of advance, with which we enter the 
group Phanerogams, we find male and female spores, producing 
male and female prothallia, and those prothallia so much reduced 
that not only do they not become separated from the asexual plant, 
but are developed within the asexual spore itself. But these same 
important characters are to be found among the highest Crypto- 
gams, and we must conclude that any line of separation is one of 
our own drawing, and has no representation in nature. 
It remains to apply to the well-known parts of any flowering 
plant the terminology that we bave been using in outlining the 
evolution of the sex-apparatus, The asexual phase, or part of the 
cycle, is “the plant” with its rich display of vegetative organs, 
Consisting of root, stem, leaves, and their various modifications. 
This asexual phase produces asexual spores of two kinds, called | 
male and female, because they are to produce male and female 
prothallia. It would be an interesting line of development 
to note the gradual differentiation of the apparatus for making 
these asexual spores, but that is aside from our purpose. The 
