336 M or pho genetic Factors 



environment, affected the expression of genes for plant height. The 

 character of growth may also be influenced. If the alga Stigeoclonium 

 is grown in relatively high osmotic concentrations, its cells round up 

 and divide in all planes to form a so-called palmella colony. In weaker 

 solutions vegetative activity is increased and the cells become cylindri- 

 cal, divide in only one plane, and form filaments (Livingston, 1900). 



Water may also affect differentiation in other ways, such as the in- 

 creased proportion of cleistogamous flowers formed as soil moisture 

 decreases (W. V. Brown, 1952; Fig. 14-8). 



A study of the water relations of plants, and especially of the forma- 

 tive effects of water on plant growth, has recently been somewhat 

 neglected. These relations provide a promising opportunity, however, to 

 approach some of the problems of plant morphogenesis from a direction 

 different from that of most experimental work today. 



