12 EVOLUTION OF PLANTS 
phytes among the higher plants, such as the common 
dodder and Indian pipe, are quite destitute of chloro- 
phyll, and hence incapable of carbon assimilation, it 
is clear that neither of these criteria can be used as 
absolutely decisive. Nevertheless, the power of car- 
bon assimilation, with the accompanying presence of 
chlorophyll, and the cellulose cell-membrane, are char- 
acters constant in all typical plants. 
As already indicated, it is near the bottom of the 
two great series of organisms that they approach, and 
as these ascending lines of development are traced they 
diverge widely, the peculiar animal and plant charac- 
ters becoming more and more pronounced as we as- 
cend. That special department of biology, known as 
Taxonomy or Classification, is the attempt to group all 
these divergent forms of life so as to indicate their 
relationships. 
So long as plants were considered as so many isolated 
objects without any genetic connection, the earlier 
systematists, especially Linné, sought simply for some 
obvious external characters which would serve for iden- 
tification, without any thought as to any real relation- 
ship. Later botanists, although they did not assume 
any genetic relationship, nevertheless in the so-called 
natural system, did make an attempt to arrange them 
in a sequence which seemed to imply some such 
connection, and, in*many instances, really succeeded, 
although, through the selection, in many instances, of 
characters of secondary importance, many mistakes 
were made. 
An ideal system of classification of plants would 
show the genealogy of the whole vegetable kingdom 
