W. A. Davis and fl. C. Sawyer 359 



iu the neighbourhood of the tuber where, by analogy with the mangold 

 and snowdrop (Parkin [1912]), the hexoses would be found probably 

 to preponderate even more than is shown in Table II. Time has 

 allowed us only to take one series of pickings with the potato, but it 

 seems highly probable that, as in the case of the mangold, sugar beet, 

 and snowdrop, the proportion of hexoses to saccharose becomes greater 

 and greater in both leaf and stalk as the season advances, and the 

 storage function becomes more and more predominant. 



As regards the transformation of the hexoses into starch in the 

 tuber, it is ijiteresting to note that in this way the hexoses are as it were 

 imprisoned and held until required for later use, when the appropriate 

 enzymes again degrade the starch to sugars. In the mangold the 

 imprisonment of the hexoses in the root is effected by their transforma- 

 tion into cane sugar. 



From data which we have obtained with many other plants, to be 

 published later, it appears that cane sugar is produced, generally in a 

 predominant proportion, in the leaf of all plants, whatever be the form 

 in which the sugars are finally stored (cane sugar, starch, inuhn or dex- 

 trose). Thus, for example, we find that, when proper precautions are 

 taken to prevent enzymic change, contrary to Deleano's [1912] recent 

 statement, cane sugar is the principal sugar of the vine leaf {Vitis 

 vinifera). In this plant the storage form is dextrose, and unless the 

 cane sugar is a primary product of the mesophyll tissue it is difficult 

 to see any special reason for its predominance in the leaf. If dextrose 

 and dextrose alone were, according to Strakosch's [1907] views, the direct 

 product of photosynthesis, one would expect to find it the principal if 

 not the sole sugar in the leaf of a plant which stores dextrose as its 

 reserve carbohydrate. In fact, as stated in our previous paper (I), all 

 the data we have obtained with plants of many different kinds best 

 harmonise with the view put forward by Brown and Morris [1893], 

 that saccharose is the first sugar formed in photosynthesis and that the 

 hexoses are formed from it and not vice versa. It seems to be the general 

 function of the mesophyll tissue to elaborate saccharose directly ; this is 

 broken down in the veins, mid-ribs and stalks, and reaches the place of 

 storage in the form of hexoses. Unless saccharose is a primary product 

 it is difficult to see why it should predominate in the leaves of plants 

 of such different types as the potato, the vine, sunflower and snowdrop, 

 in none of which is cane sugar the storage form ; there seems, indeed, 

 no useful purpose in its production at all in such cases, as the sub- 

 stances stored are undoubtedly built up from hexoses, which are the 



