SOME RECENT EXPERIMENTS. 369 



and sickly ; the colouring matter dries up, and the white, wan 

 tissue of the leaf is all that survives. The more a plant is ex- 

 posed to the light, the deeper will be its green. In a shrubbery 

 you may notice that the brown leaves of any particular ever- 

 green or bush, if so situated as to lose the direct action of the 

 sun's rays, will soon change colour. Instead of their natural 

 brightness of tint, they assume a sickly greenish-yellow hue, 

 and are said to be suffering from chlorosis. The formation of 

 the chlorophyll is obstructed, or takes place too slowly. Of 

 course, this peculiar condition will frequently arise from bad 

 soil, or a long continuance of damp weather ; but it is also the 

 result of a want of light. 



It should be observed that young leaves are always of a lighter 

 green than old j simply because the latter have been exposed 

 for a longer time to the light. And so the leaf goes on deepening 

 and deepening in colour, until the sad days of autumn come, and 

 the green gives way to yellow and brown and red, owing to the 

 influence of the changing season on the chlorophyll of the plant. 



In reference to this interesting subject, which deserves to 

 be more closely investigated, we may place before the reader 

 the results of certain recent experiments.* 



MM. Prillieux, Brongniart, and Roze (Comptes Rendus, Jan. 

 3 and 17) have made some important observations on the 

 apparently spontaneous movements of the grains of chlorophyll 

 within the leaves of plants. These had been observed by 

 Bohm to congregate under the direct action of the sun; 



* As recorded, in a condensed form, in The Academy (Feb. 12, 1870), 

 pp. 131, 132. 



2 A 



