78 



THE STRUCTURE OF ECONOMIC PLANTS 



directed attention. The latter (19) has also reviewed the literature 

 on leaf ontogeny in the angiosperms and has accompanied it with an 

 extensive bibliography. On the basis of the work that has been 



F,n . a Transection through the midrib of a tobacco leaf: ab ph, abaxial phloem; ad ph, 

 .^^U^7^^^^S^ /., epidermal hair; M P^Hsade cells; .,. spongy paren- 

 chyma; xy, xylem. 



reported, it is clear that the development of the leaf in the angk,- 

 sperm does not conform to any one pattern. The specific details, 

 concerning a relatively large number of angiosperms, show no 



