INTRODUCTION. 



19 



The nature of the growth-forms recognized by Drude has been 

 examined with a view to determining what features of plant structure 

 have been used by him as criteria for his subdivisions. The chief of 

 these criteria are Hsted in table 1, together with the divisions based 

 upon these criteria, and the environmental conditions to which these 

 features seem, in the present state of our knowledge, to be most closely 

 related. An examination of this table will show that Drude has used, 

 in the main, criteria to which a definite physiological importance can 

 be attached, or to which, in some cases, several lines of importance can 

 be ascribed. The definitions which Drude has given some of his 

 growth-forms employ the words "dicotyledonous" and "monocotyl- 

 edonous." It is difficult to decide whether these words indicate a 

 recognition of phylogenetic divisions or whether they are used as a 

 brief and convenient means of distinguishing types of stem, of leaf, and 

 of branching, which may have a physiological as well as a phylogenetic 

 significance. 



Table 1. — Analysis of the criteria used by Drude in distinguishing growth-forms. 



We are here brought to face the difficult question as to whether the 

 distinction between the dicotyledonous and monocotyledonous types 

 of stem should be maintained in a classification of this kind. Is the 

 distinction to be regarded as a purely phylogenetic one, or is there 

 sufficient difference between the physiological efficiency of these very 

 dissimilar organs of conduction and leaf display to warrant separating 

 them? A similar question is raised as to the physiological importance 

 of the parallel-veined and net-veined condition of leaves. Again, 



