232 /ngvar Jorgensen and Walter Stiles. 
sucrose is a primary product in assimilation. Although it is possible 
that all the sugar in the mesophyll cells of the leaf is sucrose, and 
that the hexoses are confined to the vascular bundles, there is no 
direct evidence of this, and there seems no sufficient reason to 
conclude that sucrose is the first sugar formed rather than that 
glucose or other hexoses first appear and that cane sugar is formed 
from them. It is no more unreasonable to suppose that sucrose 
should be formed from hexoses in the leaf when these latter reach 
a certain concentration, that to suppose starch should be formed as 
a temporary reserve carbohydrate in such leaves as those of 
Tropceolum or Potato, for as starch is a storage form in the potato 
tuber, and is similarly formed in the leaf, so since sucrose is the 
storage carbohydrate in the root of Beta, being formed from hexoses 
according to Davis, Daish and Sawyer, there is no reason why it 
should not also be formed from hexoses in the leaf. The value of 
evidence in regard to the first sugar formed in the leaf, derived from 
considerations of the variation in amount of the different sugars, is 
indicated by the fact that Brown and Morris, Parkin, and Davis, 
Daish and Sawyer all conclude that sucrose is the first sugar formed 
in assimilation, while their results in regard to the variation of 
different sugars through the day differ absolutely. Thus Brown 
and Morris found that both the sucrose and hexose content diminished 
during the day; Parkin found the hexose content remained 
practically constant, while the sucrose varied ; Davis, Daish and 
Sawyer found both the sucrose content and hexose content 
varying in the leaf, while in the veins the sucrose content remains 
approximately constant, the hexose varying widely. 
We do not wish it to be supposed that we therefore support 
the view that glucose is the first sugar of carbon assimilation. We 
hold that the data so far produced from analyses of carbohydrates 
in leaves and from microchemical examination provide insufficient 
evidence in favour of or against either theory. While we may 
regard starch as a secondary product of assimilation, and while also 
there is good evidence that carbohydrates are translocated, in some 
cases, or to some extent at any rate, as hexose sugars, and while 
there is strong evidence that sugars are the first definitely known 
products of the assimilatory process, there is no evidence at present 
as to which particular sugar is the first one to be produced in the 
leaf. 
(To be continued.) 
