84 STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



One of the most remarkable and puzzling features of the carbohy- 

 drate synthesis in the plant is the fact that the sugars found in nature 

 are confined to a small number of those which are theoretically 

 possible on the basis of stereoisomeric constitution. A conception 

 of the manner in which the plant-cell is able to synthesize carbohy- 

 drates from compounds which are already extant in the cell has been 

 suggested by E. Fischer. This is based upon the fact that in the 

 artificial synthesis of sugars from compounds containing a smaller 

 number of carbon atoms, by means of the cyanhydrine reaction, the 

 influence of existing stereoasymmetry of these carbon compounds is 

 exerted on the final product. In other words, an asymmetric carbon 

 compound yields an asymmetric product. In the same way, the 

 reactive products of the primary carbohydrate dissociation would 

 also be asymmetric substances, and these, by reaction roughly anal- 

 ogous to the cyanhydrine reaction, have the power of uniting with 

 the products of photochemical decomposition of carbon dioxid and 

 thereby yield an asymmetric product in the form of d-glucose, d-fruc- 

 tose, or its condensation product, sucrose. As these substances in 

 turn are used for the formation of the large variety of other com- 

 pounds found in plants, they would serve as the basis of the asym- 

 metry of these. 



The most noteworthy result of the energy release of respiration in 

 plants is the formation of new compounds. These compounds may 

 be of higher energy content, although they may not again serve the 

 plant as food material, but enter only into the structural or plasmic 

 elements of the organism. Or respiratory glycosis may serve the 

 plant in such a way that the primary products thereof are substances 

 on to which carbon dioxid or its primary splitting product can be 

 added to form a further supply of hexose sugars. Given, then, a 

 properly functioning respiratory system, together with the necessary 

 simpler materials and an apparatus capable of utilizing radiant 

 energy, the plant is able to manufacture not only the large variety 

 of substances found in its structural elements, but also to add organic 

 material derived from the carbon dioxid of the air. 



METHODS AND APPARATUS. 

 1. The Experimental Material. 



The experiments on the photosynthetic activity were carried out 

 with single excised leaves. For this work leaves of the Canada 

 Wonder bean and of the sunflower were used. The methods of 

 culture were the same as those employed for the material used in 

 the respiration experiments and the same precautions were observed 

 in regard to using only perfect leaves and in the method of cutting 

 and handling the leaves. These always remained in perfectly 



