190 PRACTICAL COURSE IN BOTANY 
other organs have already been noticed, as also their entire 
disappearance in certain cases (97, 101, 149) and replace- 
1a. 255.— Spearlike leaves of Spanish 
bayonet. 
perfoliate leaves bar the way 
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, 
scales, sticky exudations, 
water holders, clasping and 
to crawling insects; horny 
cuticles, as well as offensive odors, bitter secretions, and 
WN 
NS eS 
258 
Fias. 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 
