i;2 GLUCQSIDES 



amount of glucosides in the bark and other parts of plants 

 different seasons of the year. Thus in Salix and Populus 

 glucoside (salicin) is most abundant in the autumn and wint( 

 and is used up in the following spring during the period 

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

 glucoside (taxicatin), which appears principally in the youi 

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

 Pangium edule and other plants the amount of cyanogenetic 

 glucosides is greatest in young leaves, with increasing age 

 amount diminishes. 



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

 the cyanogenetic ones, are reserve food stuffs, since, if ii 

 troduced into the food materials of a plant, glucosides hai 

 an injurious effect, owing to the aromatic residues. 



Combes, f however, finds that a glucoside is toxic only to 

 plants in which it does not naturally occur ; he agrees that 

 glucosides do not furnish carbohydrate food, since plants 

 grown in an atmosphere free from carbon dioxide are unable 

 to make use of these substances. 



PecheJ 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 



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



t Combes : " Rev. gen. Bet.," 1918, 30, 216. 



^ Peche : " Sitz. Kais. Akad., Vienna," 1912, 121, 33. 



