602 



WEED FLORA OF IOWA 



LEAF PROTECTION. 



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

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

 clangers are excessive transpiration and intense light. By regu- 

 lating the opening in the stomata which are the chief passageways 



\ t\ 



Fig. 455 I 



Fig. 455 II 



Fig. 455 V Fig. 455 IV Fig. 455 III 



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

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

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

 hair of Nettle. 



(After Thome.) 



