THE HERBACEOUS DICOTYLEDONS 389 



pre-eminently the consequence of degeneracy and has no dynamic 

 evolutionary significance in contrast to herbaceous modifications 

 presented by the stems of dicotyledonous angiosperms. 



With the foregoing preliminary statement in regard to the 

 appearance of the herbaceous type in primary and secondary 

 cylinders (or in the secondary cylinder alone) in lower forms we 

 are in a position to attack the origin of the stems of herbaceous 

 texture in the highest seed plants. It has been noted in the 

 preceding paragraphs that the degenerate herb is derived from 

 ancestral forms characterized by woody stems. The same general 

 condition is found in dynamic herbaceous types among dicoty- 

 ledons; and it is extremely important to keep this situation 

 clearly in view, as a failure to do so results in an anatomical fallacy. 

 It cannot accordingly be too strongly emphasized that a proper 

 understanding of herbaceous axes in the angiosperms can be reached 

 only by the comparison of nearly related stems of woody and 

 herbaceous texture. Any other procedure leads to erroneous 

 results. 



In former chapters the various types of rays in the Gnetales 

 and the dicotyledons have been discussed. In the present con- 

 nection only one of these need seriously be considered the com- 

 pound ray. The large or compound type of ray is characteristic 

 of only a few arboreal types of probably primitive antecedents, but 

 occurs in a more or less modified form in many herbaceous and 

 climbing stems. It will be convenient to discuss first the condi- 

 tions present in vines, as these are usually more woody in their 

 character and consequently serve as an appropriate transition to 

 axes of soft or herbaceous texture. As a preliminary to the con- 

 sideration of the anatomy of the vine, it will be well to devote 

 some attention to the organization of an exotic member of the 

 Vitaceae from the tropics. Fig. 267 reproduces the woody cylinder 

 of the shrubby genus Leea from the eastern tropics. To the right 

 are to be seen a number of large rays which clearly belong to the 

 category designated in an earlier chapter as compound. Above 

 and below, and particularly to the left of the illustration, the com- 

 pound rays become much smaller in size. Those which are of 

 greater dimensions are in relation to leaf traces passing out in the 



