(»*) 
the amount of arbutin diminishes progressively, and that of hydro- 
quinone first increases, but afterwards quickly diminishes when 
assimilation begins in the young shoots. On comparison of the amount 
of arbutin in a number of plants (May 3 rd ) before the opening of 
the buds, with that after the opening (May 24 th ), taking old and 
young parts together, 22—32 % of the total was found to have 
disappeared. 
This glucoside is therefore also used in the opening of the 
buds and undergoes before use a fermentative hydrolysis, as a result 
of which hydroquinone shows itself in the tissues. The amount of 
hydroquinone is, however, much smaller than one might expect from 
the amount of arbutin which has disappeared (for 100 milligrams of 
arbutin, for instance, 6 milligrams of hydroquinone). Thus a part of 
the hydroquinone appears here to be directly worked up in meta¬ 
bolism, and the hydroquinone, which is present in the opening buds, 
also disappears again rapidly as soon as assimilation becomes vigorous. 
I therefore found only traces of arbutin in the second budding of 
some plants in August, which is nevertheless also accompanied by 
arbutinhydrolysis. 
During, the opening of the buds I often found that no arbutin 
occurs in the stem, a further proof that the glucoside is not trans¬ 
ported as such. 
In the buds of the pear-tree Riviere and Bailhache *) have demon¬ 
strated hydroquinone, and this induced me to search for a hydro- 
quinone-glucoside in this case also. Such a glucoside was indeed 
found to exist and the amount of combined hydroquinone was again 
much greater than that in the free state. The enzyme, which here 
I was also able to prepare from the young shoots, rapidly brings 
about the hydrolysis of the hydroquinone-glucoside *), so that it is 
necessary to kill the parts by boiling alcohol. Then one finds in the 
adult leaves 0.01_0.03 %, in the young shoots 0.3 % of hydro- 
quinone. In this case methylhydroquinone and methylarbutin are absent. 
The glucoside is found in the buds, leaves, wood and bark of the 
branches and also in the roots, but in the bark only. The amount 
in the root-bark is very small (0.05%); that in the wood of the 
b G. Riviere e t G. Bailhache. De la presence de l’hydroquinone dans le Poirier. 
R. de l’Acad. de Sc. P„ris GXXXIX. 1904. 
2 ) 1 could not obtain the glucoside in a crystalline form, so that I could not 
determine with certainty from the physical constants, whether it is identical with 
arbutin ; the products of hydrolysis, hydroquinone and glucose, which 1 found, 
make the identity very probable, however. 
