324 Evolution in the Plant Kingdom. 
Not so very long ago it was thought that at least one fact in 
classification was impregnable, viz., that there were two great and 
very distinct groups of plants, called Phanerogams and Crypto- 
gams. These two were set off against each other as antipodal 
groups, between which: there was nothing in common. Unfortu- 
nately, the names given to these groups were simply an expression 
of the botanical knowledge of the time. ‘ Apparent reproduction” 
‘and “ hidden reproduction” may have correctly expressed the facts 
with respect to these two groups once ; but they are very far from do- 
ing so now. The modern botanist, with his more complete appliances 
and methods, has begun to resolve the great nebulous mass of 
Cryptogams, and has discovered in it distinct systems and groups. 
The whole subject of Cryptogamic classification is, of necessity, — 
quite inchoate. Certain groups and relationships have been dis- 
tinctly defined; but among them and around them there float 
numerous hazy forms that refuse to be classified. Our knowledge 
is not sufficient to attempt the work with any degree of certainty, 
but certain broad principles have been struck out which will serve 
to guide. 
It is known now that Phanerogams form but one of several. cor- 
relative groups. The most useful scheme of classification at present 
makes the number seven. These seven primary groups must be. 
considered merely as convenient pigeon-holes i in which to distribute 
our facts. 
It is not my purpose to go into the details of any supposed order 
of evolution of the plant kingdom, but to give some general thoughts 
concerning it and to trace through the development of a single 
structure. Generalization is always easier than details; for in it 
one is never embarrassed by the facts. 
It seems probable that the plant kingdom must have begun in 
some such form as Protococcus, the common green slime found stain- 
ing foundation stones, bark, etc. It surely represents the unit of 
structure and of function in the vegetable kingdom. We can con- 
ceive of no simpler plant-form than a single chlorophyll-bearing 
cell. Some of you will recall the fact that we have unicellular 
plants without chlorophyll, such as yeast and bacterial forms; as 
well as forms called plants that seem to be mostly naked proto- 
plasm, such as slime moulds; but the former probably represent 
degraded forms, while the aniinal or plant character of the latter 
