ae 
326 Evolution in the Plant Kingdom. 
extreme complexity it seems but fair to consider it a good index 
of relative rank. I intend to give in merest outline the develop- 
ment of sexual reproduction, guarding such an attempt with the 
following statements :— 
1. This is taken as but a single striking line of development, 
and must be understood to be accompanied by many other ‘details 
in asexual reproduction and vegetative structure which bear it out 
but which we have no occasion to mention. Just as in describing 
the evolution of the horse the toes arè seized upon as the one among 
other structures most striking and most simple of presentation. 
2. There are hosts of side issues which represent departures 
greater or less from this general line of advance, and which cannot 
be taken into account in this general sketch. In general, they can 
be all explained by the law of adaptation. 
3. Even the line I propose to follow can be but imperfectly pre- 
sented ; as there is not knowledge sufficient to make it as complete 
as we would like it, and not time enough to present it as complete 
as we know it. 
Taking, therefore, this thread of sexual reproduction as a guide 
through the labyrinth of plant forms, we may come to some glim- 
mer of light. 
Naturally, the lowest group would contain those plants in which 
no sexual reproduction has been discovered. In recognition of this 
position, as well as their probable position in point of time, they 
have been called Protophytes, or “ first plants.” The lowly char- 
acter of lacking sexual reproduction is further borne out in their 
structure, for they are mostly one-celled forms. In this group 
stands Protococcus as a type, a single-celled chlorophyll-bearing 
plant with no discovered sexual reproduction ; and, as degenerate 
representatives, the bacteria and yeasts. You will notice, however 
that the definition of this group, on the basis we have adopted, is 
a negative one, being not as much what we have found, as what we 
have not found. It follows that this group furnishes a kind of 
limbo to which all one-celled plants are consigned, in case no sexual 
reproduction is found, a sort of unresolved nebulous mass, in fact, a 
cloak for ignorance. It is like the man who undertook a great scheme 
of classification, and made his two principal divisions “ things that I 
know ” and “things that I don’t know.” The first group he could 
classify reasonably well; the second he did not have to classify. 
