444 



MORPHOLOGY OF THE ANGIOSPERMS 



The remarkable ontogeny of the compound palm leaf is evidence that 

 the palms are only distantly related to other monocotyledons. It provides 

 support for the theory that the primitive angiosperm leaf was simple, 

 as shown by the Ranales. 



A 



b-b 



c- c 



d-d 



B 



I 

 I 

 a 



a-a 



r2 



b-b 



c-c 



d-a 



Fig. 148. Diagrams showing gross structure and relationship of leaf parts in well- 

 developed but still folded leaves of two types. A, B, palmate type; C, D, pinnate 

 type. B, D, longitudinal; A, C, cross sections at levels indicated in longitudinal dia- 

 grams, n, reins; p, petioe; r\ dorsal lobe of rachis; r^, ventral lobe of rachis (hastula). 

 (From Eames, 1953.) 



Within the family, the palmate type is clearly the advanced type, as 

 shown by the presence in tlie palmate forms of a strong midrib in all 

 stages of reduction, the costa. The costa shows evidence, not only in its 

 large size but in its form and vascular structure, that it represents the 



