480 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tannin ; but starch is by no means universally present. The starch 

 is not destroyed by intense white sunshine or oxygen. 



The hrpochlorin is the substance first destroyed by the action of 

 intense light, and its disappearance is the first sign of an injurious 

 influence on the cell. 



The protoplasm of the cell undergoes a change under the action 

 of intense light, as is shown by its loss of turgidity, the parietal 

 protoplasmic layer becoming more permeable to the cell-saj). The 

 rotation of the protoplasm is arrested by exposure to strong light ; 

 but it will recommence if the exposiu'e has not been too long. 



The cell-wall undergoes no material change fi'om exposure to 

 strong light. 



The general conclusions to which the investigations of Professor 

 Priugsheim have led him are : (1) That the destruction of the 

 coloui'ing matter of the chlorophyll, even in the living cell, is a 

 process of oxidation, independent of the presence of carbonic acid ; 

 (2) That its decomposition in light does not take place in a mixture 

 of carbonic acid and hydrogen of any given proportion, in which 

 assimilation and decomposition of the carbonic acid is possible ; (3) 

 that the decomposition of the colouring matter in the living plant is 

 a pathological process ; and that, when once destroyed, it cannot be 

 reproduced. He therefore still maintains his previous view that the 

 process of res2:>iration is checked rather than promoted by the 

 presence of chlorophyll, which acts by the absorption of light, 

 favouring at the same time the process of assimilation. The first 

 jjroduct of assimilation he believes to be hypochlorin ; other sub- 

 stances which are found in the chlorophyll-grain, such as starch, 

 glucose, oil, and tannin, being formed from it by oxidation. The 

 facts upon which Professor Pringsheim rests this conclusion are : 

 that hypochlorin is generally present in chlorophyll-grains ; that the 

 amount of hyi^ochlorin in a chlorophyll-grain varies inversely in 

 proportion to the amount of starch ; and the further fact that no 

 hypochlorin can be detected in seedlings until their exposure to light 

 has been sufficient to enable them to assimilate. 



Transpiration.* — A series of investigations by P. Sorauer on this 

 subject have been directed chiefly to the following points : — The 

 influence on transpiration of temperature ; the influence of light ; 

 the influence of the particular variety ; the relation to transpiration 

 of the fresh weight of the plant ; the relation of surface ; the relation of 

 the amount of water in the soil ; the influence of the moisture of the 

 air ; of the size of the root ; of manuring ; of the jDartial removal 

 of the leaves ; the transpiration of etiolated plants ; transpiration in the 

 absence of carb Dnic acid. 



The general conclusions arrived at are that transpiration is a 

 physiological and not a mechanical process ; that is, it cannot be 

 compared to a similar process in dead substances. It depends on the 



* Soraner, P., " Studien iib. Verdunstung." Mittlicil. d. pflauzenphys. Vers.- 

 Stat. am K. Pom. Inst. Preskau, iii. (18S0) pp. 351-190. 



