No. 469] BIOLOGY OF CACTI 37 



different (Figs. 12-14). These stomata are superficially [placed 



and they open directly into the suhstoinal 

 chamber (Fig. 12). Tluvsiihstoinal canal 

 of the permanent oi'-aii. ilicn'toir is l;i( k- 



the absence of j 



sionof the chlorencli vnia to ihv cpidcnni 

 The heaxy outci cpidtimal <.t tli 



older portions of lochinocactns is lici 

 replaced bv a delicate one. In conne( 

 tion with this structure of the leaves ( 

 Opuntia appears their tunction ot ))r( 

 moting transpiration, and ])resninai)l 

 the respiratory activities as well, and i 

 this they render it an important service 

 as will be apparent from the results ( 

 the transf)iration studies. 



In all of the stu.iu^ (ui tlu ti iM.pii uimm ..t , uu uiic 

 conducted outdoors tin: polvnicicr method annon :():)a). described 

 elsewhere, was eniploved. A few. liowexer, which will be pointed 



