LIMIT OF PHYSIOLOGICAL WATER 45 



In the plant house the effect of shade was to increase the 

 size of the leaves of the plant. This was especially the case 

 with rosettes of Ranunculus sceleratus, Gaura biennis and 0. 

 parviflora. 



The leaves of the shade rosettes not only had larger blades 

 and longer petioles but they were elevated to a greater angle 

 with the surface soil. It is hard to account for this fact. It 

 may be due to the stimulus of decreased light causing the 

 leaves to stretch towards the source of light. It undoubt- 

 edly increases evaporation from the leaves, thus hastening 

 the transfer of soil nutrients through the plant. A study of 

 the comparative anatomy of sun and shade leaves belonging 

 to the same species, would no doubt show essential differ- 

 ences in the arrangement of the mesoplyll, in the thickness 

 of the epidermal covering and in the comparative number of 

 stomata per unit of leaf surface. The leaves of Ranunculus 

 sceleratus were modified to a greater degree than those of the 

 other plants. 



The following table indicates the effect of shade in raising 

 the limit of available water in the soil. The shade plants 

 show an increase of 0. 8 per cent of non-available water in 

 the dry soil and of 1.3 in tne wet. The plants are put in two 

 groups ; those grown in dry loam, plot P-II, and those in 

 wet, plot P-I. The amount of available water in the for- 

 mer varied from to 10 per cent, in the latter from 10 to 30 

 per cent. 



