W. A. Davis, A. J. Daisii and G. C. Sawyer :311 



this test is at all characteristic of ketoses is still an open question. 

 Strakosch and Neuberg [1904] consider that it is, but Ofner [1904 and 

 1905] and Ost [1905] regard it as unsatisfactory in presence of dextrose. 

 With regard to Senft's [1904] test for dextrose which Strakosch relied 

 upon it is perhaps sufficient to point out that Strakosch himself admits 

 that '"die Unterscheidung von Rohrzucker und Glucose nach dem 

 Senftschen Verfahren ist an die richtige Schatzung des untersuchenden 

 Auges gebunden^." Absolutely in contradiction with Strakosch's views, 

 but in accord with our own, are the earlier micro-chemical observations 

 of de Vries [1897], who found in the chlorophyll-containing cells of the 

 sugar beet no reducing sugars at all, in the general tissue of the vascular 

 bundles only small C[uantities, but in the larger vessels and veins 

 increasing quantities of hexoses. 



Strakosch rehes almost entirely on his micro-chemical tests. He 

 quotes only two quantitative estimations of the sugars ; in one, an 

 extract of mesophyll tissue was found to contain 0-15 per cent, of 

 hexoses and 0-02(3 per cent, of saccharose ; in the other, an extract of 

 vein tissue contained 0-12 per cent, of hexoses and 0-54 per cent, of 

 saccharose. No details are given as to the preparation of these extracts, 

 nor of the means taken to prevent enzyme changes. The results 

 given absolutely contradict those obtained by Kayser [1883], Girard 

 [1884], Ruhland [1911], Parkin [1912], Colin [1914] and ourselves, 



^ Since the above was written Mangliam (Aminli Bol. 1915, 29, 309) has pubhshed 

 some observations on the osazone method of locating sugars in plant tissues. As a result 

 of his experiments he considers (p. 377) that any attempt to distinguish saccharose 

 qualitatively in presence of its hexose constituents by Senft's method cannot give trust- 

 worthy results. Senft was led to attach too much importance to this method from 

 the results obtained with .50 per cent, sugar solutions, and neglected to check them with 

 weaker solutions comparable in concentration with the contents of plant cells. Mangham, 

 therefore, Uke ourselves, considers that Strakosch's technique was unrehable and "only 

 those of his conclusions with regard to cane sugar which were founded on evidence other 

 than that derived in the above manner can be regarded as at all trustworthy." This 

 would leave very little of the structure raised by Strakosch still standing. 



It is difficult to understand llangham's view that it is possible to discriminate between 

 dextrose and laevulose by means of the osazone test, seeing that both sugars {as well 

 as mannose) yield identically the same osazone : Mangham seems to regard the osazoues 

 from dextrose and laevulose as distinct substances. 



In the writer's opinion httle reliance can be placed on a micro-chemical osazone test 

 as a means of identifying maltose in plant tissues, owing to the presence of large quantities 

 of other sugars. Our quantitative analyses (some 500 in all) have in no single instance 

 disclosed the presence of even traces of maltose in the leaves or conducting systems of 

 plants. In work of this kind, micro-chemical tests as a means of distinguishing individual 

 sugars should be avoided and only quantitative methods adopted. Otherwise contradictory 

 and uncertain results are inevitable. [Note added, Dec. 9, 1915.] w. A. D. 



