164 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



the assimilating to the storing tissues is maintained by the 

 conversion of sugar into starch in the latter. 



It must be pointed out that there is some uncertainty 

 as to the accuracy of conductivity measurements upon sap 

 pressed from small roots, owing to the adhesion to them of 

 particles of clay. Washing is not permissible in such cases, 

 as there is the possibility of dilution of the sap taking place 

 if the cells are not at their maximum degree of turgidity, 

 as well as of the adherence of water. 



SEASONAL VARIATIONS IN THE OSMOTIC PRESSURE AND 

 ELECTRICAL CONDUCTIVITY OF PLANT ORGANS. 



Several attempts have been made to correlate the varia- 

 tions in pressure with external conditions, such as amount 

 of sunlight, temperature, or rainfall. 



Trinchieri (1909) has given both tables and graphs illus- 

 trating the behaviour of Salpichroa rhomboidea throughout 

 the year. The rhizomes, cortex and entire organ, upper 

 and lower portions of the stems, and the leaves, were all 

 examined. The rainfall, too, was shown in a graph. He 

 took plants both from a shady position in a Coniferetum 

 and from ground formerly used as a vineyard. As a general 

 rule slightly higher values were obtained from the plants 

 growing in the sunny position in the Naples Botanic 

 Gardens. The fluctuations are very considerable in all 

 the organs. Since such a number of factors are concerned, 

 it is not easy to single out the influence of any one as of 

 especial importance. 



Dixon and Atkins (1912, 1, 2 and 3) also studied the annual 

 variations in the leaves and roots of Ilex aquifolium, and 

 of the leaves of Hedera helix and Syringa vulgaris. 



No correlation could be discovered between the fluctua- 

 tions in pressure and the rainfall. This is not surprising, 

 as the cells are normally fully distended. The results of 



