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 Linn^, 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 



