206 PHOTOSYNTHESIS 



of the carbohydrates of the leaves of Trapaeolum is composed of maltose; 

 from their analyses as high as 50 per cent in some cases. They identified 

 the maltose by means of the maltosephenylosazone and made quantitative 

 determinations of this sugar by means of a differential in the copper re- 

 ducing power of the sugar mixture. Other workers have also reported 

 varying amounts of maltose in leaves. Lewis and Tuttle "° report as high 

 as 1.21 per cent of the expressed sap of leaves of Tyrol a rotimdifolia and 

 slightly less for Populus treinuloidcs and Linnaea borealis, though the 

 amount varies greatly with the season. From the work of Brown and 

 Morris it is evident that a great deal of importance is to be attached to 

 sucrose as a possible first product of photosynthesis. This has raised two 

 leading questions : first, whether the sucrose arises from the maltose, and 

 second, whether the maltose is actually present in the living leaf or whether 

 it is formed from the starch during the preparation of the leaf material 

 for analysis. 



Parkin'^ has made analyses of leaves of the snowdrop (Galanthus 

 nivalis), a plant which does not normally form starch in its leaves. He 

 was unable to detect any maltose, but considerable sucrose. 



There is no doubt that the preparation of leaf material for analysis, 

 particularly the drying, is apt to be a source of error, as is discussed in a 

 later portion of this chapter. In the process of drying there is the possi- 

 bility that enzymes continue to act on certain carbohydrates for some time, 

 and that some enzymes are more easily destroyed than others. Thus, if 

 maltase is destroyed sooner than diastase, the latter would continue to 

 Ijreak down starch to maltose, the latter sugar would not be hydrolyzed 

 to glucose and there would be an accumulation of maltose. "- 



There are few reliable methods for the direct identification of maltose, 

 as maltose behaves very much like glucose towards most reagents. Mal- 

 tose has a higher rotation (+ 137-138°) than glucose (-f 52.7°). Maltose 

 also reduces cuproalkaline solutions, and on hydrolysis yields two mole- 

 cules of glucose. After hydrolysis the rotation of a solution containing 

 maltose decreases and the reducing power increases. This has been the 

 basis of most quantitative determinations of maltose. In the presence 

 of sucrose the inversion is carried on first with invertin, which effects 

 sucrose and then with acid, which hydrolyzes maltose, and a differentiation 

 can thus be arrived at. Application can also be made of the Barfoed 

 copper acetate solution and of iodine solutions." 



'"Lewis and Tuttle, Ann. of Bot., 34, 405 (1920). 



"Parkin, Biochem. Jour., 6, 1 (1911). 



"Davis and Sawyer, Jour. Agri. Sci., 7, 352 (1916). 



"Brown and Morris, 1. c, 663. Hinkel and Sherman. Jour. Am. Chem. Soc, 

 29, 1744 (1907). Cajori, Jour. Bio. Chem., 54, 617 (1922). Fellenberg, Mitt. 

 Lebensm. Hyg., 11, 129 (1920). Geelmuyden, Zeit. anal. Chem., 48, 137 (1909). 

 Castallani and Taylor, Jour. Trop. Med., 25, 41 (1922). It should be mentioned 

 that whenever iodine is used as a reagent, either in the determination of glucose or 

 starch, it must be borne in mind that much plant material contains substances which 

 absorb iodine. These substances are probably phosphatides, the unsaturated fatty 

 acids of which take up iodine very readily. This is a frequent and very trouble- 



