172 GLUCOSIDES 



amount of glucosides in the bark and other parts of plants at 

 different seasons of the year. Thus in Salix and Populus the 

 glucoside (salicin) is most abundant in the autumn and winter, 

 and is used up in the following spring during the period of 

 flowering and seed formation ; also in the case of Taxus the 

 glucoside (taxicatin), which appears principally in the young 

 shoots, is greatest in amount in the autumn and winter. In 

 Pangium edule and other plants the amount of cyanogenetic 

 glucosides is greatest in young leaves, with increasing age the 

 amount diminishes. 



Guignard * does not believe that glucosides, or at any rate 

 the cyanogenetic ones, are reserve food-stuffs, and the fact 

 that, if introduced into the food materials of a plant, gluco- 

 sides have an injurious effect, owing to the aromatic residues, 

 gives some support to this contention. 



A contrary opinion is held by Peche,-|- who holds that 

 hydrocyanic acid is a direct product of photosynthesis ; some 

 of it combines with sugar to form a glucoside, and some is 

 transported in a labile form, probably in a loose combination 

 with tannin, and stored for future use as food in various 

 tissues. 



The occurrence of certain glucosides, especially in places 

 of active metabolism such as leaves and young shoots, may 

 indicate that certain bye-products are fixed, either temporarily 

 or more permanently, in this form. 



In conclusion it may be stated that many may perform a 

 biological function ; thus the bitterness or poisonous nature 

 of the glucosides or of the products of hydrolysis, other than 

 sugar, may serve as a protection against herbivorous or fruit- 

 eating animals ; the antiseptic properties of these dissociation 

 products may have a value in preventing the development of 

 disease organisms in parts which may be damaged, e.g. seeds, 

 leaves and bark. Some may play a part in connexion with 

 the secretion of sugar by extrafloral nectaries, for it appears 

 that the basal cells of these structures, together with the ele- 

 ments of the adjacent tissues, are rich in glucosides. 



•Guignard: "Compt. rend.," 1905, 141, 236; 1906, 143, 451, 

 fPeche : " Sitz. Kais. Akad., Vienna," 1912, 121, 33. 



