THE EFFECT OF MOISTURE 



263 



midity of 10 per cent, it has almost ceased. In the 

 observations made by Gain,* the fresh weight of the en- 

 tire plant was determined. Seeds of various species 

 were planted in soil containing either from 3 to 6 per 

 cent, of water, or from 12 to 16 per cent. Growth was 

 more rapid in the damp than in the dry soil, so that the 

 weight of the full-grown plant was 1.12 times greater 

 in the radish, 2.23 times in the bean, and 2.7 times in 

 the flax. 



The effect of a dry soil and atmosphere is well shown 

 by the characters of desert plants. These are stunted 

 in growth, and are of a nearly uniform gray colour, ow- 

 ing to their intense hairiness. The leaves are more 

 fleshy, and there is a great tendency to the formation 

 of spines. That these characters are in part at least 

 the direct result of want of water is shown by the 

 fact that they may disappear if an abundance of water 

 is supplied. Thus Ononis spinosa. L., if grown in a 

 rich, well-watered soil, or in a moist atmosphere, gradu- 

 ally loses its spines, those first formed under the new 

 *Ann. Sci. Nat. Bot. (7), xx. p. 63, 1895. 



