190 



PRACTICAL COURSE IN BOTANY 



other organs have already been noticed, as also their entire 

 disappearance in certain cases (97, 101, 149) and replace- 

 ment by other parts; it is 

 unnecessary, therefore, to 

 revert to this branch of the 

 subject here. 



207. Protective modifica- 

 tions. The most general 

 protective modifications 

 that leaves undergo are 

 (1) for the conservation of 

 moisture, as explained in 

 202, and (2) for protection 

 against animals. Many of 

 the adaptations for the 

 former purpose serve inci- 

 dentally for defense against 

 animals also. Spines, hairs, 



FIG. 255. Spearlike leaves of Spanish scales, Sticky exudations, 



water holders, clasping and 



perfoliate leaves bar the way to crawling insects ; horny 

 cuticles, as well as offensive odors, bitter secretions, and 



256 



257 



258 



FIGS. 256-258. Protective hairs magnified : 256, mullein ; 257, cinque-foil 

 258, Shepherdia. 



poisonous juices warn leaf -eating cattle and bugs away. 

 These devices are merely protective, however, and adapted 

 to a passive attitude of self-defense. 

 208. Insectivorous leaves, But sometimes a plant 



