ii6 Carbon Assimilation. 



From these results Brown and Morris conclude that cane 

 sugar is the first sugar formed in the leaf and that this functions as 

 a temporary reserve which accumulates during active assimilation. 

 When the concentration of cane sugar reaches a certain amount, 

 any excess of sucrose is converted into staixh in the chloroplast. 

 The cane sugar, on being translocated from the leaf, is inverted into 

 glucose and fructose, while the starch is hydrolysed and translocated 

 as maltose. That it is not hexoses that are the first sugars formed 

 in the assimilatory process is indicated by the fact that after 

 assimilating all day, leaves still attached to the plant contain no 

 glucose and very little fructose. The cane su^ar, on the other hand, 

 has remained almost constant while starch and maltose have both 

 decreased. In the case of the cut insolated leaves it is supposed 

 that translocation is to all intents stopped. Under these circum- 

 stances the cane sugar and starch both increase greatly, but the 

 glucose very little. 



The results given in Table XXXI indicate that in the dark 

 the cane sugar and starch both decrease in amount, while the 

 glucose and fructose have both increased in amount. As presumably 

 the sucrose is hydrolysed into equal quantities of glucose and 

 fructose, and the latter appears much in excess of the former. 

 Brown and Morris conclude that glucose is largely used for ' 

 respiration in the leaf. 



However, from what we have already said on the reliability of 

 the measurements of glucose and fructose, it is extremely doubtful 

 whether the recorded values of glucose and fructose have any 

 meaning. Moreover, Davis and Sawyer (1916) have been unable 

 to find maltose in Trcpceolutn majus and they conclude that the 

 maltose found by Brown and Morris in their extracts resulted from 

 the degradation of starch by diastatic enzymes after maltase in the 

 leaf had been destroyed. 

 2, Snowdrop {Galanthus nivalis, L) (Parkin). 



The snowdrop possesses the very usual monocotyledonous 

 characteristic of not forming starch in the leaves. Hence 

 as already indicated, the analysis of sugars is simplified. 

 Parkin's results were obtained from observations made over a 

 number of years. In most cases only the values of sucrose and 

 hexose are given, no attempt bein}» made, except for a special 

 purpose, of distinguishing between the hexoses. Parkin's results 

 are the most clearly stated of all the accounts we have of leaf 

 carbohydrates and it is possible from the numbers he gives, to 



