260 



PLANT PHYSIOLOGY AND ECOLOGY 



pots so that they may be grown without competition to serve 

 as checks. When the plants become well grown and in actual 

 competition, light readings are made for two or three leaves of 

 the most successful competitors and of the least successful ones 

 and their starch content is also determined. From these figures 

 the light intensity and starch content are determined for the 

 total leaf area of each plant, and these results are checked by the 

 control plants. 



The relation of water to competing plants is a more difficult 



Fig. 104. Competition cultures in the plant-house. In the foreground 

 is a mixed culture of Solidago and Onagra. 



task to study. It is necessary to determine the water available 

 for the control plant, together with its w^ater loss. These must 

 also be determined for the competing individuals, and the two 

 results compared. The water content is found for a block of 

 the soil 2 or 3 decimeters square. The water loss of the plants 

 in it can only be ascertained by cutting the block out and weigh- 

 ing it from time to time, or by sinking a pot or box in the plot 

 at the beginning, and removing it when necessary. 



