418 



HOW PLANTS PROTECT THEMSELVES 



390. Cutting leaves. Some grasses and sedges are generally 

 avoided by cattle because of the sharp, cutting edges of their 

 leaves, which will readily slit the skin of one's hand if they are 

 drawn rapidly through the fingers. Under the microscope the 

 margins of such leaves are seen to be regularly and thickly sel 

 with sharp teeth like those of a saw (Fig. 320, c, d). 



d 



FIG. 320. Stinging hairs and cutting leaves 



a, stinging hairs on leaf of nettle ; 6, bristle of the bugloss ; c, barbed margin o 

 a leaf of sedge ; d, barbed margin of a leaf of grass. All much magnified. 

 After Kerner 



391. Weapons of desert plants. In temperate regions, where 

 vegetation is usually abundant, such moderate means of protec- 

 tion as have just been described are generally sufficient to insure 

 the safety of the plants which have developed them. But in 

 desert or semi-desert regions the extreme scarcity of plant life 

 especially exposes the few plants that occur there to the attacks 



