248 GLUCOSIDES 



desirable. According to Clark and Gillie,* the salicin content 

 of samples of bark of Salix sitchensis from British Columbia 

 varied from 2-8 per cent in the autumn to 7-38 per cent in 

 the spring. 



Weevers f suggests that the salicin formed in the leaves 

 during the daytime is hydrolysed at night, the glucose being 

 translocated away, while the saHgenin, which remains behind 

 in the leaf, is recombined with sugar the next day ; the object 

 of the glucoside formation would appear to be the production 

 of a difficultly diffusible compound of sugar. 



MONOTROPITIN. 



This glucoside was discovered by Bridel % in Monotropa 

 hypopitys, and also in the fresh roots of Spircsa Ulmaria, S. 

 filipendula and 5. gigantea § ; the same author also showed 

 that gaultherin, occurring in the back of Betula alba, was 

 identical with monotropitin. The glucoside, from whichever 

 source obtained, is hydrolysed by the same enzyme variously 

 described as gaultherase, betulase, or primeverase, which also 

 occurs in Monotropa, giving methyl salicylate and the glucoxy- 



lose primeverose. 



AUCUBIN. 



The darkening of the tissues on drying of Aucuba, Melam- 

 pyrunt, and Rhinanthus, and many other plants, is due to one 

 and the same glucoside aucubin, which is acted upon by 

 emulsin, which also occurs in the plant yielding an aglucan, 

 aucibigenin, of unknown constitution. The darkening of the 

 tissues is due to the oxidation of the aucibigenin. The colour 

 change may be readily brought about by wounding or ex- 

 posing the tissues to chloroform vapour. 



The similar darkening occurring in Orobanche is due to 

 direct oxidation of a non-glucosidal material contained in the 

 plant, the darkening taking place without previous interven- 

 tion of a hydrolytic enzyme (see below). 



* Clark and Gillie: " Amer. J. Pharm.," 1921, 93, 618. See also 

 Brown : " Pharm. Journ.," 1903, 16, 588. 



t Weevers : " Rec. trav. bot. Neerl.," 1910, 7. 

 X Bridel : " Bull. Soc. chim. biol.," 1923, 5, 918. 

 § Bridel : id., 1924, 6, 679. 



