THE METABOLISM OF PLANTS. 147 



not, however, confined to the chlorophyll-corpuscles, for Holle found that 

 it was also generally diffused throughout the protoplasm of the cells. The 

 formation of the oil is doubtless to be attributed to the action of certain 

 conditions which were unfavourable to the formation of starch from 

 proteid and which led to the decomposition of protoplasm in such a way 

 that oil was one of the products. In fact Godlewski found that when 

 an abundant supply of carbon dioxide and exposure to bright light were 

 ensured, starch-grains were abundantly produced in the chlorophyll- 

 corpuscles of the leaves, especially the younger leaves, of the Musaceae. 



Pringsheim has found that a substance which he terms Hypochlorin 

 can be made to appear in chlorophyll-corpuscles by treating them with 

 dilute acid. No analysis of this substance has as yet been made, but it 

 probably contains either no oxygen, or less than a carbohydrate. He 

 regards this substance as the first visible product of constructive meta- 

 bolism in the corpuscle, but this requires proof. The substance may be 

 merely a product of the decomposition of chlorophyll by the acid. 



The conditions essential to the formation of non-nitro- 

 genous organic substance from carbon dioxide and water by 

 the chlorophyll-corpuscle are briefly these ; exposure to light, 

 of some considerable intensity, and a sufficiently high tem- 

 perature. De Saussure came to the conclusion that the pre- 

 sence of free oxygen is essential to the process, for he found 

 that green plants soon die in an atmosphere of pure carbon 

 dioxide, and that plants which can live for a time in an 

 atmosphere of nitrogen, die when a proportion of carbon 

 dioxide, which would have been beneficial if added to ordinary 

 air, is added to the nitrogen. Boussingault carefully re-inves- 

 tigated the subject, and found that the effect of the presence 

 of any other gas, not in itself hurtful, upon the absorption of 

 carbon dioxide is simply a mechanical one (see p. 73). 



The various processes which result in the formation of 

 starch in the chlorophyll-corpuscles are gone through rather 

 rapidly, especially in the more lowly-organised plants. Thus 

 Kraus found that starch-grains made their appearance in the 

 chlorophyll-corpuscles of Spirogyra within five minutes after 

 exposure to bright sunlight, within two hours in diffuse day- 

 light ; in Funaria they made their appearance after two hours' 

 exposure to sunlight, and after six hours' exposure to diffuse 

 daylight. 



The great physiological difference between plants which 



IO 2 



