5 o THE SYNTHESIS OF CARBOHYDRATES 



probability, to the closure of the stomates resulting from the 

 accumulation of materials which were produced at a greater 

 rate than that at which they could be translocated. 



Kostychew and his collaborators * found that the photo- 

 synthesis of Arctium and Phragmites on bright warm days 

 reaches a maximum several hours before sunset, usually in 

 the forenoon ; which maximum is followed by a marked re- 

 tardation owing to the removal of the products of the operation 

 not keeping pace with the formation of new material. An 

 increase in weight of approximately 0-15 gram per 300 sq. cm. 

 of leaf surface is enough to end photosynthesis. When the 

 conditions of photosynthesis are not so favourable, for example 

 in dull weather, the sudden retardation of the process is not 

 observable. Similar results were obtained in the study of 

 various aquatic plants. f It was also found that various 

 algae, e.g. Mougeotia, Spirogyra, Cladophora and Rhizoclonium, 

 exhibit different assimilation intensities which are invariably 

 greater than those of aquatic phanerogams, e.g. Ceratophyllum, 

 in spite of the fact that the latter generally contain a larger 

 quantity of chlorophyll per gram of dry weight. These ob- 

 servations, together with those of McLean alluded to on an 

 earlier page (p. 24), indicate that the phenomenon is widely 

 spread. 



With regard to the oxygen evolved, since carbon assimi- 

 lation by green leaves is unaffected by various concentrations 

 of oxygen in artificial atmospheres, and since the oxygen 

 pressure of the internal atmosphere of plants is a very variable 

 quantity, it would not appear that the amount of oxygen is 

 a limiting factor of any great significance. 



THE ORGANIC PRODUCTS OF CARBON ASSIMILATION. 



The ultimate products of carbon assimilation are carbo- 

 hydrates : Brown and Morris, % in their classical work on the 

 chemistry and physiology of foliage leaves, identified sucrose, 



* Kostychew, Kudrivzewa, Moissegewa and Smirnowa : " Zeit. wiss. 

 Bot.," 1926, 1, 679. 



t Kostychew and Soldatenkow : id., 1926, 2, 1. 



\ Brown and Morris : " Journ. Chem. Soc," 1893, 63, 604. 



