ALLIED AND MISCELLANEOUS PRODUCTS 179 



be universal in small amounts. When hydrolyzed they yield a 

 hexose and another substance known as a sapogenin (saponin 

 former). This may be illustrated by the hydrolysis of digitonin 

 from Digitalis which yields digitogenin, glucose, and galactose: 



C54H 9 2028 + 2H20=C3oH4806 + 2C 6 Hi206 + 2C6Hi206. 



digitonin digitogenin glucose galactose 



The flavone and anthocyan glucosides may be better considered 

 with the pigments. 



Physiological Significance of Glucosides. — With so many 

 different kinds of glucosides it is not reasonable to expect that 

 all will have the same function in the plant. This wide variety of 

 substances undoubtedly has an equally wide variety of functions, 

 among which may be mentioned the following: 



1. They act as sources of reserve food because of the sugars 

 they contain. Their occurrence especially in seeds lends support 

 to this view. In bitter almonds the glucoside is hydrolyzed during 

 germination, when the free HCN can be detected; and in Prunus 

 laurocerasus, during periods of starvation these glucosides dis- 

 appear. The increase of the glucosides during periods of photo- 

 synthesis also points toward this function. In the willow, salicin 

 is formed during the day and is split up at night, according to 

 Weevers (1910). The saligenin remains in the leaf to be used the 

 next day, while the glucose is translocated, to other parts of the 

 plant. Not only is there a daily variation in the amount of gluco- 

 side but a seasonal one as well. In Salix, Populus, Taxus, and 

 Vaccinium the glucoside is most abundant in the fall and winter, 

 dropping to its lowest levels in the spring when the new shoots 

 form. 



2. Guignard (1906) does not think that the cyanophore gluco- 

 sides can be used as reserve foods because of the toxic action of 

 the HCN, but inclines rather to. the view that these glucosides 

 fix injurious by-products either permanently or temporarily in 

 this form. The occurrence of glucosides in young shoots and leaves 

 where metabolism is active is explained on this basis, and the 

 large percentage of glucosides in some plants during unfavorable 

 conditions gives support to this waste-product theory. 



3. Peche (1912) thinks the glucosides are direct products of 

 photosynthesis. Some are stored for future use while others, more 

 labile, are quickly broken down. The relation of these products 



