OSMOTIC PRESSURES AND ELECTRICAL CONDUCTIVITIES 163 



that the more massive roots function largely as storage 

 organs, for in them the pressure of the non-electrolytes 

 attains considerable dimensions, as can be seen in the table. 



It may here be remarked that though the leaves of Ilex, 

 gathered at the same time as the samples of the roots, 

 always possessed higher pressures, yet the conductivity of 

 the young leaves was considerably below that of the roots. 

 The oldest leaves, on the other hand, contained a far greater 

 quantity of electrolytes than did the roots. 



This progressive change in the character of the sap on 

 passing from the roots to the leaves may be illustrated by 

 the following figures obtained with Iris germanica, the 

 entire plants having been dug up and examined: 



TABLE XLI. 



Iris germanica, NOVEMBER 15. 



Here the osmotic pressure decreases from above down- 

 wards, but the electrical conductivity increases, with the 

 exception of that of the rhizome. The tops of the leaves 

 are appreciably richer in sugars than the bases, though 

 their osmotic pressure is the same. As is well known, Iris 

 stores no starch in the green portions of the leaves, except 

 a negligible quantity in the guard cells of the stomata. 

 In the white portions of the bases of the leaves starch is, 

 on the contrary, plentiful, as also in the rhizome and roots. 

 It appears that the gradient of sugar concentration from 



