INTERNAL FACTORS 49 



amount of potash equivalent to two hundredweight of potas- 

 sium sulphate per acre. 



The superiority of the plants treated with potassium sul- 

 phate is associated with a more rapid translocation of starch 

 from the leaflets. 



The Products of Carbon Assimilation. — Much investi- 

 gation is necessary before the precise significance of this factor 

 can be determined : of the products of carbon assimilation, 

 carbohydrate and oxygen are the most conspicuous. 



It is well known that, according to the law of mass action, 

 chemical action diminishes as the products of the activity 

 accumulate ; the initial rate can only be maintained provided 

 the initial proportions of the reacting substances are preserved 

 and the products of the reaction removed. In the leaf a further 

 complication arises since sugar is an osmotic substance and its 

 undue accumulation may lead to a physical disturbance in the 

 synthesizing machine such, for example, as the closure of the 

 stomates. This may be averted by the conversion of the sugar 

 into starch, a marked and well-known phenomenon in many 

 plants, which temporary reserve is translocated at nightfall 

 after hydrolysis. But a great accumulation of starch may 

 inhibit photosynthesis in that, presumably, it reduces the 

 effective surface of the chloroplasts which, according to Briggs, 

 Warburg, Wurmser and others, is the seat of the primary 

 photochemical action. Translocation is most apparent in the 

 dark, but it takes place also by day and it is only in sugar leaves 

 that the undue concentration of soluble carbohydrates, owing to 

 hindrances to rapid translocation, or to a high assimilatory effi- 

 ciency, is likely to prove an important factor in carbon assimila- 

 tion. Broock * found that the leaves of the sugar beet on 

 bright sunny days showed a rapid increase in their dry weight 

 up to midday, at which hour there was a sudden decrease : this 

 loss in weight was more or less uniform until about midnight. 

 The sudden drop in the carbon assimilation at noon indicates 

 that the process was brought to a standstill owing, in all 



* Broock : " liber tagliche und stiindliche Assimilation einiger Kultur- 

 pflanzen," Halle, 1892. See Thoday : " Proc. Roy. Soc," B, 1910, 

 82, 443. 



VOL. II. — 4 



