328 The Dextrose- Laevidose Ratio lit the MaiKjohl 



removed from the sap of the stalks in forming new tissue, iaevulose 

 being the sugar specially adapted to this purpose. Lindet in a recent 

 paper [191 IJ, inspired by the results of his earlier work, cites experi- 

 ments made vnt\\ yeasts which also serve to show that Iaevulose lends 

 itself to reproductive growth or new tissue formation better than 

 dextrose. 



Parkin [1912] in experiments on the snowdrop leaf found that 

 in 47 out of 52 analyses the Iaevulose was in excess of the 

 dextrose ; representing Iaevulose as unity, in these cases the ratio varied 

 from 1 : 0-4 to 1 : 0-76. In the five remaining cases, the ratio was 

 1 : 1-01 to 1 : 1-06. The ratio of Iaevulose to dextrose appeared to rise 

 during the night, that is when photosynthesis is in abeyance; the 

 excess of Iaevulose was always greatest in the lower (colourless) part 

 of the long snowdrop leaf. To explain his results Parkin also adopted 

 Brown and Morris' view that the dextrose lends itself most readily 

 to the respiratory needs of the plant, whilst the Iaevulose is used largely 

 in constructive work such as the building up of the plant's framework. 



As was pointed out by Brown and Morris in 1893 the correctness of 

 the dextrose and Iaevulose values depends entirely on the accuracy of 

 the readings of the rotatory power; a shght error in these makes a 

 large difference in the apparent proportion of the two hexoses. The 

 main purpose of the present paper is to show that, whilst it is possible 

 to take the actual readings very accurately (in our case the probable 

 error did not exceed 0-005°), the values are falsified, in the case of most 

 plant material, by the presence of optically active substances other than 

 the sugars, which are not completely precipitated by the basic lead 

 acetate (or other defecating substance) used to purify the solutions. 

 T3^pical substances of this kind are amino-acids and amides, such as 

 glutamic acid and glutamine, aspartic acid and asparagine. The first 

 three of these have a pronounced positive rotation which is greatly 

 enhanced by acids, whilst asparagine is laevo-rotatory in aqueous 

 solution and dextro-rotatory in acid solution. The influence of these 

 substances in falsifjnng the results obtained by the method of double 

 polarisation for the cane sugar in the molasses of sugar manufacture 

 has been studied by several chemists, more particularly by II. Pellet 

 (compare Dosage du Sucre par Inversion, 1913), but the effect of these 

 and other impurities on the results obtained for the dextrose : Iaevulose 

 ratio in plant material has not hitherto been taken into account. 



We find in the mangold, just as Lindet did in the sugar beet, that the 

 dextrose always seems to be in excess of the Iaevulose, especially in the 



