40 NATURE OF DESERT PLANTS 



this territory was a bare, sun-cracked plain swept by hot, dry 

 winds. Not a green leaf was to be seen. Heavy rains trans- 

 formed this level tract of land into an inland sea. In a few days 

 the water disappeared and one morning he was surprised to see 

 green blades appearing everywhere and in a few days the barren 

 earth was covered with an almost tropical profusion of vegeta- 

 tion and bright flowers. Many desert plants to be sure develop 

 permanent aerial parts but here, too, the most striking feature 

 is the extreme reduction of the organs. Compare the areas of 

 the Spanish bayonet, aloes, grease wood and sage with that of 

 our leafy plants. The cactus represents one of the extreme forms 

 of reduction. The leaves have been dispensed with entirely and 

 are not represented save possibly by the spines. Consequently 

 the work of the leaves devolves upon the stems. But even 

 with the reduction of surface and the development of thick- 

 ened, epidermal cells, cuticle, hairs, wax, etc., which cause 

 the tough, leathery character of the organs, these plants would 

 not be able to withstand the drying heat of the desert were 

 it not for the fact that the cells are rich in mucilaginous 

 substances and various salts which effectually retain the water. 

 While desert plants receive very meager amounts of water, 

 this is so well protected that the plants are usually rich 

 in water. Drinking water is frequently obtained in desert re- 

 gions from cacti by pounding up the pulpy interior and squeezing 

 out the water. Animals are well aware of this rich storehouse 

 and will eagerly devour the cacti after the spines are burned off. 

 The development of these storage cells accounts for the fleshy 

 character of many alkaline, saline, and desert plants. Curiously 

 enough there are many examples of xerophytic plants living in 

 bogs and marshes, as, for example, the rushes and sedges, the 

 horse tail ferns (Equisetum), the lamb kill (Kalmia) and leather 

 leaf (Chamcedaphne} , etc. The cause of the association of these 

 plants with aquatic forms is not known. In exposed moors and 

 heaths these reduced forms would have decided advantage be- 

 cause of their protection against drying winds. Our sedges and 

 rushes are exposed to very intense heat and light which may 

 possibly cause so heavy a transpiration that these plants are not 



