CLASSIFICATION OF VASCULAR PLANTS 63 



evolutionary relationships. Such a classification is a summary 

 of all of our knowledge of plants — structure, development and 

 life history, physiology, ecology and even bio-chemistry. For 

 all of these are at once causes and effects of the evolutionary 

 process. This is why classification must be ever changing, ever 

 adjusting itself to new knowledge. 



A classification must also be a convenient tool for all botanical 

 workers. This demands simplicity. An ideal arrangement 

 would be dichotomous. At any rate, coordinate groups must 

 not be too numerous. There must be an adequate but not 

 cumbrous terminology, and this must be consistently used. 

 Groups should be monophyletic, and should be natural. Where 

 these ideals are not compatible, which will very often be the 

 case, it must remain a matter of opinion whether one or another 

 principle shall prevail. On main points, however, we are now 

 in position to expect substantial agreement. 



The old distinction between Cryptogams and Phenogams is 

 well nigh extinct. And yet it is useful for certain purposes, and 

 should be used without apology in those cases where it is needed. 

 There is no better means of distinguishing those plants which 

 are disseminated primarily by spores from those which are dis- 

 seminated by seeds. The distinction has become ecological 

 rather than morphological, although of course the seed plants 

 are descendants of spore plants. These two terms may no 

 longer be used for elementary teaching. They belong only to 

 peculiar situations, in the vocabulary of advanced students. 



No apology is necessary for eliminating the terms endogen 

 and exogen. One would have thought that as taxonomic divi- 

 sions of seed-plants they had entirely dropped out of sight, had 

 not a recent elementary book of considerable merit brought them 

 again into print. Requiescant in pace. 



It looks now as though Pteridophyta and Spermatophyta 

 should also be committed to the history books and advanced 

 laboratories. That the boundaries between these groups is 

 hopelessly broken down is indicated by the fact that Engler 

 places the Cycadofilicales in the former group, and Jeffrey 

 places them in the latter. We could still retain these terms if 



