12 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



small increase in mean molecular weight in the last two 

 experiments is probably due to the production of maltose, in 

 the unfiltered sap and intact leaves, at a rate sufficient to 

 mask the decrease due to inversion of sucrose and respiration 

 of the hexoses. The fall in pressure of the unfiltered as 

 compared with the filtered sap is explicable by the action 

 of respiratory enzymes. Such comparisons between the 

 analyses of sugar content on the one hand, and determina- 

 tions of osmotic pressure and mean molecular weight on 

 the other, serve to impress one with the delicate balance 



TABLE V. 



Syringa vulgaris : LEAVES. 



maintained by the living cells of the leaf throughout' the 

 cycle of chemical transformations taking place from day 

 to day. 



IDENTIFICATION or SUGARS BY MEANS OF PHENYL- 



HYDRAZINE AND ITS DERIVATIVES. 



The identification of sugars in plant tissues was later 

 studied by Senft (1904), who employed phenylhydrazine 

 with aqueous acetic acid. As is well known, glucose and 

 fructose afford the same phenylosazone, which crystallizes 



