32 



season, whilst the saccharose remains practically constant. In passin^^ 

 from leaves to mid-ribs, from mid-ribs to the tops of the stalks, and 

 from the tops of the stalks to the bottoms, the ratio of hexoses to 

 saccharoses steadily increases. As the season advances the pre- 

 dominance of the hexoses in leaf, mid-ribs and stalks becomes more 

 and more marked. 



The proportion of hexoses to saccharose in the leaf tissue follows 

 the temperature curve closely during the day time. 



The facts brought forward can apparently be best explained by 

 Brown and Morris' view that saccharose is the primary sugar formed 

 in the mesophyll of the leaf under the influence of the chlorophyll ; it 

 is transformed into hexoses for the purpose of translocation. This 

 transformation occurs in the veins, mid-ribs and stalks, the proportion 

 of hexoses increasing more and more as the root is approached. The 

 sugar enters the root as hexose and is therein reconverted into 

 saccharose ; once in this form the saccharose is not able to leave the 

 root until it is put under contribution for the second season's growth. 



These views are in accord with de Vries' micro-chemical observations 

 as to the nature of the sugars in the different tissues, but entirely in 

 contradiction to those of Strakosch, which are considered to rest on 

 no secure foundation. 



They also agree with Parkin's results with the snowdrop, with 

 Pellet's analyses of the sugar cane, with Collins' results with the sugar 

 beet, and the authors' observations on other plants, such as the vine 

 (Vitis vinifera), potato, dahlia, etc., which store carbohydrates in other 

 forms (dextrose, starch, and inulin). 



As regards the mechanism by which saccharose is synthesised from 

 the hexoses, it is improbable that this change is effected by invertase 

 by a process of reversible zymo-hydrolysis. The entire absence of 

 invertase from the root is against this view. 



XIX. " Studies of the Formation and Translocation of Carbo- 

 hydrates in Plants. ''^ 11. — " The Dextrose-lcBvulose Ratio 

 in the Mangold'' William A. Davis. Journal of 

 Agricultural Science, 1916. 7^ 327-351. 



Previous observers have always found more laevulose than dextrose 

 in the leaves of plants and, as they have assumed that the two sugars 

 are formed in equal proportions from the inversion of cane sugar, it 

 seemed to follow that dextrose was more readily put under contri- 

 bution for the respiratory processes of the cell than is Isevulose. The 

 value of the analytical results, however, depends entirely on the 

 readings of the rotatory power, and any small error is considerably 

 magnified in the final calculation. 



The author shows that the readings are completely falsified by the 

 presence of optically active substances other than sugars, which are 

 not entirely removed by the preliminary purifying processes. 



At present it is not possible to determine with accuracy the pro- 

 portions of dextrose and kevulose in different plant tissues, nor is it 

 possible to draw any conclusions as to their functions in the plant. 

 Some tentative determinations have been made which, while not 

 entirely correct, probably show the type of variation which the sugars 

 undergo. The results agree with the assumption that dextrose and 

 laevulose occur in equal proportions in the leaves, stalks and roots, 

 being formed by inxcrsion of the saccharose in the leaf ; they then 



