74 Cellulose 



flowering plants, the variations of diastatic activity with the con- 

 ditions of assimilation, and the relations of diastase to the starch 

 and sugars (including maltose) present in the leaves lead to the 

 important conclusions which we give in the words of the original : 



' Looking at the results all round, they are, it seems to us, 

 decidedly opposed to the view that either dextrose or levulose is 

 the first sugar formed by assimilation, and point to the somewhat 

 unexpected conclusion that, at any rate in the leaves of Tropaeolum, 

 cane sugar is the first sugar to be assimilated by the assimilatory 

 processes. There seems every reason to believe that this cane 

 sugar . . . functions in the first place as a temporary reserve 

 material, and accumulates in the cell sap of the leaf-parenchyma 

 when the processes of assimilation are proceeding vigorously. 

 When the degree of concentration of the cane sugar in the cell 

 sap and protoplasm exceeds a certain amount, which probably 

 varies with the species of plant, starch commences to be elaborated 

 by the chloroplasts, this starch forming a somewhat more stable 

 and permanent reserve material than the cane sugar, a reserve to 

 be drawn upon when the more easily metabolised cane sugar 

 has been partially used up.' 



From these authors' experiments it also appears that, in the 

 translocation of the sugar through the leaf stalk into the stem, it 

 takes the form of dextrose and levulose. The former, however, 

 being more quickly used up in the respiratory process, there is a 

 larger proportion of the latter passing over into the general 

 metabolic circulation. 



The starch, on the other hand, migrates in the form of maltose, 

 and this appears to be, in a sense, a starvation phenomenon that is, 

 it is only put under contribution to the general supply of nutrient 

 material when, and in proportion as, the carbohydrates of lower 

 molecular weight are used up. 



These researches obviously constitute an important advance 

 towards the elucidation of the elaborating functions of the plant 

 cell. What the actual first step may be in the building up of 

 tissue-substance, is still a matter of conjecture. The prominent 

 facts presented to us are, (i) that carbonic anhydride is decomposed 

 in the plant cell, the whole of the carbon being retained, and part 

 of the oxygen restored to the atmosphere ; (2) that this decomposi- 

 tion takes place under the influence of the protoplasmic contents 



