( 200 ) 
etiolated budding branches and with bisected leaves (the halves of the 
leaf being compared in the evening and in the morning). In etiolated 
budding the catechol increase and salicin decrease were in the ratio 
36:100; in leaves the nocturnal increase of catechol was to the 
decrease of salicin in the ratio 31 :100 (for 2000 leaves), which 
agrees sufficiently well with the hypothesis. 
It is not until the salicin content of the bark becomes great 
(6 a 7 °/ 0 ) and equals that of the leaves, that the salicin ceases to 
diminish in the leaves overnight and the catechol no longer increases, 
the glucose transport of the hydrolysed salicin then seems to have 
stopped. Whether the salicin concentration influences the transport, 
or whether the concentration gradient of the glucose does so, remains 
for further investigation. 
In order to determine also the populin present in the bark of 
Salix purpurea I used a press-juice obtained from Aspergillus niger, 
which was precipitated by an excess of alcohol. The precipitate 
contained a mixture of various enzymes, among which is one which 
completely hydrolyses populin, as was sftown by experiments on the 
pure glucoside. 
In addition, the mixture of enzymes also contained emulsin, 
invertin and maltase; in order to utilize this mixture for the quan¬ 
titative determination of populin the increase of reducing sugar 
after the action of the Aspergillus enzyme was to be diminished 
with that, obtained after the action of emulsin, invertin*) and maltase ). 
As might be imagined the method only gives useful results, when 
the populin is present in large quantity, for in the glucose-values 
found for populin all the errors of the other determinations accumu¬ 
late, and these errors can never be completely excluded in the case 
of hydrolysis by enzymes. 
The method cannot therefore be applied to Salix purpurea, where 
the populin is quantitatively unimportant. It was found, however, 
that populin is formed in large quantity in the normal young 
shoots but is, on the other hand, wholly absent from etiolated shoots; 
this is the reason why in the etiolated budding the ratio of salicin 
to catechol agrees so much more closely with that which mig t 
expected theoretically. . 
I also attempted to determine populin quantitatively in opu “ 
species, but did not obtain good results, because the populin con e 
is too small in 4he species I have hitherto examined, viz: P- 
!) Salix purpurea contains small quantities of saccharose in the leaves 
a ) The extract had been obtained from the parts with warm wa er ' g 
been treated with lead acetate, so that it did not contain any starch or 
