Physiologie. 441 



verte, est im phenomene trop fondamental, pour ne pas admettre 

 qu'il debute partout de la meme maniere. Aussi peut on invoquer 

 en faveur de mon hypothese que le nombre de plantes pour les- 

 quelles on constate la presence d'acide cyanhydrique va continuelle- 

 ment en augmentant. Mais il faudra toujours expliquer comment 

 dans la grande majorite des plantes, le metabolisme ne comporte 

 pas d'arret au Stade cyanhydrique." Th. Weevers. 



Weevers, Th., The physiological significance ofcertain 

 glucosides. (Proc. Kon. Ak. v. Wet. Amsterdam 1909.) 



This paper contains a continuation of a treatise reported in the 

 Bot. Centr. 1903. p. 621. The validity of the supposition that the 

 Compounds of benzene derivatives with carbohydrates serve to form 

 substances not easily diffusable was tested on arbutin, the glucoside, 

 which accompanied by traces of methylarbutin occurs in Ericaceae. 

 From Vaccinium vitis idaeae an enzym was obtained, by which 

 arbutin is rapidly hydrolysed into glucose and hydroquinone. 



Arbutin plays the part of a reserve material, which is princi- 

 pally deposited in the leaves. Before the opening of the buds no 

 hydroquinone or merely a trace is present in the leaves and the 

 same applies to the stems and roots, which latter at this period also 

 contain but traces of arbutin l ). 



With the development of the young shoots the amount of arbutin 

 diminishes and that of hydroquinone first increases but afterwards 

 diminishes as soon as assimilation begins in the young leaves. 

 The glucoside is used in the opening of the buds and undergoes 

 before use a fermentative hydrolysis as a result of which hydro- 

 quinone shows itself in the tissues. The amount of hydroquinone is 

 much smaller than one might expect from the amount of hydrolysed 

 arbutin, for a part of the hydroquinone seems to be directly worked 

 up in metabolism. 



In different parts of the pear tree a glucoside, probably identical 

 with arbutin, which by the enzym isolated from the young shoots 

 is rapidly hydrolised into glucose and hydroquinone, was demon- 

 strated. The glucoside was found to increase during the day and to 

 diminish during the night. Latter diminution is accompanied by an 

 increase of hydroquinone. During the summer the arbutin is depo- 

 sited in the bark to be used up in, the formation of new shoots in 

 spring. All that season the amount of free hydroquinone is greatly 

 increased by fermentative arbutin-hydrolysis and the decrease of ar- 

 butin was to the increase of hydroquinone in the proportion of 100:40 

 that of the molecular weights, in other words the whole aromatic 

 product remains localised in the cell and is worked up afterwards, 

 when assimilation has begun. Pfeffer's hypothesis is also confirmed. 



From voung shoots of Salix piirpurea a salicin-splitting enzym, 

 which in 1902 the author had already surmised was obtained. This 

 salicase also obtained from Populus canadensis is not identical with 

 emulsin nor with amygdalase; some experiments pointed to a rever- 

 sible action. The aromatic Splitting product saligenol could be detec- 

 ted in the young shoots during some days in May only: never it 

 could be found in the bark although this absense is not due to a 



l ) A method of quantitative determination of arbutin and hydroquinone was 

 worked out. 



