President's Address. 307 



contained bodies is involved in a discussion of the function 

 of the apparatus. 



Two series of phenomena exhibited by the chlorophyll 

 apparatus, or its parts, under the influence of light, are of 

 importance. Firstly, h olio tropic phenomena are exhibited. 

 As Bohm first observed, the corpuscles in daylight coat the 

 upper and under surface of the cell- walls of horizontal 

 leaves, and in darkness are only found on the side walls, 

 producing thereby a variation in intensity of colour on the 

 surface of the leaves. Secondly, chlorophyll and the 

 contents of the corpuscles are constantly undergoing de- 

 struction and reformation. As regards the colouring 

 matter, this destruction is a local effect due to light (yellow 

 rays), as Batalin, Sachsse, Askenasy, and others have 

 shown. Leaves become yellow under this process owing to 

 the more sensitive cyanophyll portion of the chlorophyll 

 having been destroyed. The destruction is supposed to be 

 a process of oxidation. This is not to be confounded with 

 tinting of leaves in autumn. The reconstruction of the 

 colouring matter is dependent upon the nutrition of the 

 plant, and is thus involved in the question of the function 

 of the chlorophyll. As regards contents of the corpuscles, 

 Sachs first showed how starch disappears during the night 

 and appears during the day, and oil globules also dis- 

 appear. 



What is the physiological significance of the chlorophyll 

 apparatus, has been, and is still, a question of mucli dis- 

 cussion. Sprengel and Turpin, who supported the vesicular 

 theory (globuline they termed the corpuscles), considered 

 each corpuscle an Alga, and these by division and apposi- 

 tion formed tissues. Amici and Dutrochet recognised in 

 the corpuscles the scattered elements of a difi'used nervous 

 system. By all other observers tlie apparatus has been 

 associated with the vegetative life of the plant, and it has 

 been generally assumed that its property is to separate in 

 light the carbon from the CO2 of the atmosphere, the C 

 then combining with the elements of water forms a substance 

 which is applied to the purposes of the plant's growth, the 

 being given off. Sachs first termed this assimilation — 

 we now speak of it as carbon-assimilation. It is a feeding 

 process, and must be carefully distinguished from respira- 



