602 



WEED FLORA OF IOWA 



LEAF PROTECTION. 



Such an important organ as the leaf, witli its delicate active tissue 

 well displayed, is exposed to numerous dangers. Chief among these 

 dangers are excessive transpiration and intense light. By regu- 

 lating the opening in the stomata which are the chief passageways 



Fig. 455 I 



Fig. 455 II 



Fig. 455 V Fig. 455 IV Fig. 455 IH 



Fio. 455. Some protective structures of leaves and stems. I. One-celled hair 

 of the Pelargonium. II. Multicellular hair of Geranium. III. Scale of 

 Oleaster (Elaeagnua). IV. Prickle from common Hop. V. Stinging 

 hair of Nettle. 



(After Thom6.) 



