WATER REQUIREMENT AND ADAPTATION IN EQUISETUM 13 



stood beside each other in the greenhouse bench so that they 

 were subjected to the same conditions of temperature, humidity 

 and light. The intensity of light in another group of plants 

 was varied by placing plants in a muslin shade tent which cut 

 down the light to 0.3% as measured by a photometer. Plants 

 in the bench receiving normal sunlight in the greenhouse, or 50% 

 full sunlight, served as checks. 



A study of the position of the stomata was made according 

 to the method worked out by Lloyd (1908:22). Thin slices of 

 epidermis were cut out from the surface and plunged into abso- 

 lute alcohol. Before using, the sections were transferred to a 

 saturated solution of Congo red in absolute alcohol. After 

 several days they were examined under the microscope. The 

 stain deeply colored the cell walls so that the opening between 

 the guard cells is easily observed. 



Cross sections of the stems which had grown under varying 

 soil-water contents for four months were made with the freezing 

 machine and examined for structural modifications. Strips of 

 epidermis were also studied for the number of stomata. 



(To be continued) 



