1914] 



OTIS 



SPIRA 



481 



stomatal surface is not equally effective, owing to the sheathing 

 habit and consequent crowding of the leaves, while in the pickerel- 

 weed and arrow-head a similar decrease in transpiration is caused 



350 



m 



jG 



CHART VI. 



® 7*r_2-*o*3tiaD-3 Be 



CQ *-*CQ >rl\ ,J| >vH 



... TS " 1 





8 



10 11 12 13 



14 15 16 17 X 19 

 AUGUST 



20 



1 



21 22X 24 



9 10. 



25 26 27 28 29 



30 



by shading and by hindrance to air movements by the closely 

 growing leaves and petioles. This might explain in a measure, or 

 at least have some influence on, the differences in transpiration 

 rates for different species. 



