60 Physiologie. 



poses of storage and is not able to leave the root until it is utilised 

 for the second season's growth. Pentoses form only a small Pro- 

 portion of the total sugars in the tissues; they are probably formed 

 from the hexoses and appear to be precursors of the pentosans. 



W. E. Brenchley. 



Davis, W. A. and G. C. Sawyer, Studies ofthe formation 

 and translocation of car.bohydrates in plant s. 3. The 

 carbohydrates ofthe leafand leafstalks ofthe potato. 

 The mechanism of the degradation of starch in the 

 leaf. (Journ. Agric. Science, p. 352—384. 1916.) 



Brown and Morris have taken the view that maitose is the 

 translocation form of starch; if so it should be found in the stalks 

 of a plant which forms starch in its leaves. These experiments, 

 however, shcw that maitose is entirely absent from the leaves and 

 stalks of the potato at all hours ofthe day and night. Theundoubted 

 presence of maitose in extracts of Tropaeoluni leaf is attributed to 

 the fact that the leaf material was dried in an oven before the 

 sugars were extracted, so that while the maltase was rapidly 

 destroyed the other enzymes were left free to act on the starch 

 resulting in the formation of maitose. In these experiments the 

 material was at once dropped into boiling alcohol and ammonia so 

 that all enzymes were instantly destroyed, and no maitose was 

 then found. This leads to the conclusion that maitose was not for- 

 med in the tissue of the leaf as such during growth, but was pro- 

 duced by the degradation of starch by the diastatic enzymes re- 

 maining after the maltase in the leaf had been destroyed in the 

 first stages of the drying process. It is considered that at the end 

 of the day the reserve starch is hydrolysed completely to dextrose 

 by the leaf enzymes, which contain an abundance of maltase. 



Saccharose is probabl}'^ the first sugar formed in the leaf; it is 

 gradually inverted on its way through the veins, midribs and 

 stalks, the inversion becoming more complete as the tuber is ap- 

 proached. The amount of Saccharose in the leaf increases during 

 the first part of the day, approximately following the temperature 

 curve, and then falls in a linear curve. Very small amounts of 

 hexoses are present in the leaf. During the time the amount of 

 Saccharose is increasing comparatively little starch is formed from 

 the hexoses. After the cane sugar maximum has been reached, the 

 hexoses begin to increase, probably on account of the hydroh^sis of 

 Saccharose to invert sugar. Dextrin or soluble starch is now first 

 detected in the leaf, and it increases regularly for about four hours 

 to 6 p. m.; at this time the true starch also reaches its maximum 

 value. Both true and soluble starch fall rapidly after this time tili 

 soon after midnight \^xy little is left. Starch is apparently converted 

 directly into dextrose. 



The true proportion of dextrose and laevulose cannot be deter- 

 mined owing to the presence of optically active impurities which 

 vitiate the Polarimetrie data It is however possible that in the 

 stalks the dextrose is actually in excess and that the starch in the 

 tuber is built up from this sugar. W. E. Brenchley. 



Hamorak, N., Beiträge zur Mikrochemie des Spaltöff- 



