WATER REQUIREMENT AND ADAPTATION IN EQUISETUM 41 



results obtained the experiment was repeated three times with 

 twenty plants. The difference in the amounts of water lost are 

 shown in the graph in figure 5. 



Fig. 5. Graph showing the effect of soil water content on transpiration. 



The plants growing in mud lost the most water while those in 

 soil of 35% water content lost the least. 



(4) Stomatal behavior 



Equisetum hyemale has 36 stomata per square millimeter of 

 surface while Equisetum fluviatile has 118. In both cases the 

 stomata are sunk in grooves resembling the modifications of a 

 xerophyte. A set of readings on the position of the guard cells 

 in the epidermis of Equisetum hyemale at 8 a.m., 12 noon, and 

 4 p.m. and an hourly series from 10 p.m. to 3 a.m. showed no 

 difference in the size of the opening between the cells. During 

 the night epidermis from both old and young stems were taken. 

 This fixed position of the stomata explains why Equisetum can 

 lose so much water per unit area by transpiration and guttation. 



