240 Sydney Mangham, 
might be great, yet at any one moment this sugar might be present 
only in such small amount as to escape detection even by very 
careful extraction methods. 
In the course of my own work—not primarily directed towards 
the determination of sugar changes in leaves—no evidence for the 
presence of maltose in anything but very small total amounts has 
been found. What has been regarded as in all probability maltose 
phenylosazone has been seen as a rule in small numbers of isolated 
parenchymatous cells of leaf veins, and in the sieve-tubes of the 
veins, for the most part the finest veins. 
I can well believe that such amounts could easily escape 
detection by methods involving extraction of leaf pulp, but I feel 
as the result of spending much time in observing many sections of 
plant tissue after treatment with Senft’s reagent, and in examining 
controls with pure sugars, that often maltose really can be detected 
in this way. I have, however, never been able to demonstrate its 
occurrence in anything in the least like the amount in which 
hexoses occur. Indeed, the scarcity of maltose was formerly the 
cause of considerable surprise in view of the results described by 
Brown and Morris. 
It should be almost unnecessary to insist that my papers on 
the osazone method dealt with the results of work by means of 
which it was sought to ascertain the degree of reliability of Senft’s 
reagent for diagnostic purposes. 
This work has shown that by the use of Senft’s reagent alone 
it is not possible to distinguish with certainty the individual sugars 
of a mixture, still less to determine the proportions in which they 
are present. 
While the reagent fails to furnish an ideal microchemical 
sugar test suitable both for qualitative and quantitative work, yet 
its use in certain forms of research is of considerable value, pro¬ 
vided that its limits are always kept in mind, and that so far as 
conclusions with regard to individual sugars are concerned the 
results yielded are regarded as indicating probabilities rather than 
as affording demonstrations. 
At the present stage of inquiry into the nature of the changes 
undergone by carbohydrates in foliage leaves, etc., it would be as 
well to try to get the most out of all available means of attacking 
the problems met with, in the hope that eventually sufficient 
evidence may be accumulated and collated to enable conclusions 
to be drawn with less uncertainty than is as yet possible, in spite of 
the vast amount of laborious work which has been carried out. 
