So 



General Botany 



in the year, plants have great difficulty in securing water. The 

 perennial plants have various ways of conserving water from one 



Fig. 45. Resurrection plant (Selaginella) of Texas and New Mexico. During the rainy 

 season the plant spreads out and grows as a rosette. When drought comes, it dries out and 

 curls up into a ball, as shown at the right. 



rainy period to the next. The barrel cactus has no leaves at all, 

 and the stem is a thick cyhnder composed largely of water-storage 

 tissue ; it may hve without additional water for two years or 

 longer. Some of the desert shrubs have leaves during the rainy 

 periods only, and these fall as soon as the drought comes. Still 

 others, like the agaves, have very thick, leathery leaves with much 

 internal water-storage tissue and a very low transpiration rate 

 (Fig. 48). 



Adjustment to desert conditions by ability to withstand drying. 

 Another group of plants is adjusted to desert conditions by being 

 able to withstand complete drying. The resurrection plant of 

 Texas is an example of this group (Fig. 45). During the rainy 

 season it is green and has its many scale-leafed branches spread 

 out, making possible food manufacture and growth. When 

 drought comes, the plant dries out and its branches curl upward 

 until it is in the form of a ball. In this condition it may be blown 

 about by the wind and remain dormant for weeks or months, 



