372 Carbohydrates of the Leaf of the Potato 



varies from 1'52 to 1-75) is best explained as in the case of the mangold 

 by the view that in the leaf the saccharose is a primary product and 

 is converted into hexoses for purposes of translocation. 



Pentosans and Matter Insoluble in Alcohol. 



In the stalks of the potato, unliko the leaves, practically no starch 

 is present to interfere with the paralipjism of the curves sho\ying the 

 pentosan content and the total leaf matter insoluble in alcohol (cellulose 

 + lignified tissue) (see P'ig. 2). From 6 a.m. to 2 p.m. the sugars and 

 other substances soluble in alcohol are increasing so that the proportion 

 of matter insoluble in alcohol falls. It should be noted that in the potato 

 stalks the sugars form only a small proportion of the increase of total 

 soluble matter; thus between 6 a.m. and 2 p.m. their increase is only 

 0-8 per cent., whilst the other soluble matters increase by 3-8 per cent.' 

 After 2 p.m. the insoluble matter gradually increases to practically its 

 earlier value, and the same is true of the pentosans. 



The following table (Table III) gives a comparison between the potato 

 and the mangold as regards the range of variation of the total sugars 

 and of the matter soluble in alcohol in the leaf and stalk. 



As regards the leaf constituents this table shows that the potato 

 in its early stages of growth closely resembles the mangold at a corre- 

 sponding stage ; the range of variation of the sugars and of the 

 substances soluble in alcohol is nearly the same in both cases. In both 

 cases also the saccharose is greatly in excess of the hexoses. It is prob- 

 able that, in the potato as in the mangold, during the later period of 

 growth, when storage is the principal function, the relative proportion 

 of saccharose and hexoses would be found to change, the hexoses then 

 predominating in the leaf as well as in the stalks. 



In the potato stalhs, however, the actual proportion of substances 

 soluble in alcohol is considerably less (.'55-2-39-7) than in the nuingold 

 (43-4-46-8), but the range of variation during the day is greater. The 



^ In the mangold stalks during the day the increase of the sugars is considerably 

 greater than the increase of the total substances soluble in alcohol; during this period 

 the soluble substances other than the sugars (amino-acids, tannins, amides) fall off greatly 

 relatively to the sugars. Thus : 



Mangold Stalks. Series I. August 26tli-27th (average of top and bottom halves). 

 Increase of total sugars from 6 a.m. to noon = 487 % 



Increase of total alcohol-soluble substances = 3-0 % 



Mangold Stalks. Series II. September lOth-Ilth. 



Increase of total sugars from 10 a.m. to 4 p.m. = 6-20 % 

 Increase of total alcohol-soluble substances =1-5 % 



