196 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



Here the graph has two cusps one in summer and one 

 in winter and corresponding depressions in spring and 

 autumn.* The relation of the concentration found in the 

 root to that of the stem is reversed, for while in deciduous 

 trees the sap solutes of the wood are generally greater in 

 the stem than in the root, the converse was found to hold 

 in the case of Ilex. Only in winter was it less in the root 

 than in the stem. 



CONCENTRATION OF NON-ELECTROLYTES. 



The form of these curves is not greatly altered if we 

 deduct from each observation the amount of depression 

 due to the electrolytes. Hence they convey a fair im- 

 pression of the variations in the concentration of the 

 soluble carbohydrates in the tracheae, and it has not 

 been thought worth while to plot special graphs for the 

 latter. 



From inspection of the tables it is quite clear that, 

 except occasionally in the summer and autumn, the molec- 

 ular concentration of the carbohydrates in the transpira- 

 tion stream in deciduous trees is greater than that of the 

 salts. Furthermore, since the sugars have high molecular 

 weights (glucose 180, sucrose and maltose 342), the actual 

 percentage weights of these substances in the sap must 

 be far greater than that of the electrolytes, which have 

 low molecular weights and are largely ionized. Hence 

 we must admit that the translocation of carbohydrates is 



* It is difficult to correlate the variations in concentration in the sap 

 of Ilex with the periods of bud expansion. The period for bud expansion 

 appears uncertain, especially in pruned or lopped trees; thus, in the 

 season 1912-13 buds expanded from November to January. In 1914 

 the summer buds were opening as early as April 22, and expansion was 

 complete about the beginning of June. On the whole, however, most 

 buds open during the winter and summer months. 



