288 ECOLOG Y. 



plants in the variation of water-supply; for example in dry 

 periods when the soil becomes dry, observe how much 

 more quickly some plants wilt than others on bright days. 

 Observe the difference in the character of the leaves of 

 these different plants, and determine what peculiarity of the 

 leaf in the one case favors the loss of water, while in the 

 other case water is conserved, or the leaf does not lose 

 water readily. 

 With reference to the adaptations of plants to the giving 



off of water, or of conserving water, Shimper divides 



them into three classes: 



1. The Xerophytes; plants which love dry places, or 



usually grow in dry places. They possess means 

 for conserving water, or for checking rapid trans- 

 piration. ' The plants are either perennial or 

 annual, and the leaves are not easily wilted. In 

 some of the plants the leaves are absent, or rudi- 

 mentary or reduced to spines, as in the cacti. 

 The larger number of the xerophytes occur in dry 

 regions. 



Xerophytic structures. Some of the xerophytic 

 structures are thick and succulent stems, or 

 leaves; leaves with a thick cuticle, with a thick- 

 ened epidermis; covering for the leaf, or stem, in 

 the form of hairs or scales: narrow thick leaves; 

 inrolled edges of leaves; the stomates are often 

 protected by being sunk in deep cavities. 



2. The Hygrophytes; plants which love damp situations, 



or grow in damp or wet situations. They possess 

 means for giving off water, or for ready transpira- 

 tion; there is a large water content usually in the 

 tissues. Hygrophytes are perennial or annual. 

 The leaves are easily wilted. 



3. The Tropophytes; the plants usually grow in tem- 



perate regions. They possess means for conserv- 



