NATURE OF PLANTS 45 



devour the cacti after the spines are burned off. The develop- 

 ment of these storage cells accounts for the fleshy character of 

 many alkaline, saline, and desert plants, many of which depend 

 upon organic compounds lodged in their cells for the retention of 

 water rather than upon the development of cutin. 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 {Chamaedaphne), 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 

 because 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 

 able to meet the loss by root absorption. This is the more 

 probable because in many instances the absorption of water by 

 plants living under such conditions is slow owing to lack of 

 oxygen and to the concentration of the water in which the roots 

 grow. 



