446 Mr. D. Thoday. Experimental Researches on [Mar. 1. 



and its rate graduallj^ decreases. This decrease may be due to the fall iu 

 temperature which took place during the night. As a whole, however, the 

 lower rate cannot be explained in this way, as the temperature was rather 

 higher than on August 18-19. It is probably to be correlated with the 

 slower growth of the tuberous roots so late in the season or their approaching 

 repletion with stored reserves. 



There remains for consideration the question whether translocation began 

 after the closure of the storaata, or whether it was practically continuous so 

 so long as reserves were present to be translocated. 



There seems to be little reason for supposing any connection to exist 

 between the closure of stomata, or cessation of assimilation, and the 

 initiation of translocation. 



The only evidence which might be taken to bear against the view that 

 translocation takes place during assimilation has reference to the formation 

 of diastase in leaves. Brown and Morris* have found that diastase is 

 formed in increasing amounts as translocation proceeds in the dark, and 

 they have been able to find no signs of its activity in the starch of 

 actively assimilating leaves. They suggest, therefore, that no dissolution 

 of starch takes place while starch formation is in progress. This view is, 

 however, quite consistent with the supposition that translocation of a part 

 of the soluble sugars, which are formed in photosynthesis, takes place at 

 the same time as another part is condensed into starch. If, as they have 

 suggested, the secretion of diastase is to be regarded as a sort of " starvation 

 phenomenon " which sets in only when the quantity of soluble sugar is 

 diminished, the formation of a superabundance of sugars during assimilation 

 would be sufficient to inhibit diastase secretion, even though translocation 

 were proceeding at the same time. Indeed, in expressing their views on the 

 periodicity of diastase secretion. Brown and Morris seem to imply the 

 continuity of the translocation of soluble sugars. 



Moreover, it must not be forgotten that the products of photosynthesis are 

 not translocated only in tlie form of sugars, l)ut that proteids also are formed 

 in the leaves. 



The high rate of assimilation iu Broocks' e.xperimcuts tells at first sight 

 against concurrent translocation. Broocks' results for August 18 indicate, 

 as they stand, an average rate of increase between G a.m. and noon of 1 7 milli- 

 gramuiCH per hour per sfjuare decimetre. Introducing a moil(!ratc correction 

 for shrinkage, the value remains still as liigh as about 14 milligrammes. If 

 we assume that translocation proceeded during this same period at the same 



* Loc. rit. 



