HOW PLANTS PROTECT THEMSELVES 



351 



420. Weapons of Desert Plants. — In temperate regions, 

 where vegetation is usually abundant, such moderate 

 means of protection as have just been described are gener- 

 ally sufficient to insure the safety of the plants which have 

 developed them. But in desert or semi-desert regions the 



Fig. 247. — Stinging Hairs and OuUing Leaves. (All mucli magnified.) 



a, stinging hairs on leaf of nettle ; b^ bristle of the hugloss ; o, bathed margin 



of a leaf of sedge ; d, barbed margin of a leaf of grass. 



extreme scarcity of plant life exposes the few plants that 

 occur there to the attacks of all the herbivorous animals 

 that may encounter them. Accordingly, great numbers of 

 desert plants are characterized by nauseating or poisonous 

 qualities .or by the presence of astonishingly developed 

 thorns, while some combine both of these means of defense. 



