SYNTHESIS OF THE CARBOHYDRATES. 25 



where x represents the chlorophyl. As a matter of fact, Gautier 

 and Timiriazeff succeeded in obtaining such a hydride protophyttin 

 which turned green on exposure to air, or in an atmosphere of 

 carbon dioxide under the influence of sunlight ; while in the dark, 

 or on exposure to sunlight in an atmosphere of hydrogen, no change 

 occurred. The existence of this body in etiolated plants, more- 

 over, has likewise been established. 



By a process of polymerization and subsequent hydrolysis, then, 

 formic aldehyde gives rise to the large number of carbohydrates 

 which are found in the vegetable world. Of the manner in which 

 these polymerizations and subsequent changes are brought about, 

 however, we know little ; but there is reason to believe that they are 

 largely effected through the activity of special ferments, as has been 

 indicated. That some of these changes take place in the chlorophyl- 

 bearing parts of the plant can readily be demonstrated. If a spiro- 

 gyra, for example, is exposed to sunlight after having been kept in 

 darkness for some time, so as to remove any sugar that may have 

 been present in the cell, it will be observed that after a very few 

 minutes starch granules appear, which can readily be- detected by the 

 addition of a little iodine solution. On subsequent removal from 

 the light the starch soon disappears from the green parts of the 

 plant, and is carried to the storage-cells proper, where it is trans- 

 formed into dextrin, glucose, and various soluble gums, which may 

 be further transformed into celluloses, certain mucilages, etc. 



Glucosides. Closely related to the carbohydrates proper, the 

 origin of which has just been considered, is a group of substances 

 which likewise occur widely distributed in the vegetable kingdom. 

 These are the so-called glticosides. They are so termed from the 

 fact that glucose is invariably formed during their hydrolytic 

 decomposition, which, as an anhydride, thus constitutes an integral 

 part of their molecule. This observation at once suggests their 

 origin also from formic aldehyde. 



Such substances are salicin, which on hydrolytic decomposition 

 yields glucose and saligenin ; arbutin, which yields glucose and 

 hydroquinon ; phloridzin, which gives rise to glucose and phlore- 

 tin, etc. 



(1) C B H 18 T + H 2 = C 7 H 8 2 + C 6 H M 0, 



Salicin. Saligenin. Glucose. 



(2) C 12 H 16 7 + H 2 == C 6 H 6 0, + C 6 H 12 6 - 

 Arburtin. Hydroquinon. Glucose. 



(3) C 21 H 24 10 + H 2 == C 15 H M 5 + C 6 H 12 6 . 

 Phloridzin. Phloretin. Glucose. 



Especially interesting is a group of glucosides which are nitro- 

 genous in character, and thus stand, as it were, midway between the 

 carbohydrates and the albumins. A study of their decomposition- 

 products hence permits an insight into the manner in which the 

 albumins are synthetically produced, and shows that here also alde- 

 hyde groups play an important part. As in the case of the albti- 



