314 



LECTURE XIX. 



per square metre ^ At an}- rate, the numbers mentioned give an approximate idea of 

 the enormous amount of work which the crown of foliage of a tree, such as 

 a Horse-chestnut, Walnut, etc., must do in the course of a summer. In these 

 cases the main mass of the products of assimilation is deposited in the form of 

 wood; whereas in Peas, Beans, and cereals, a great portion of it passes into 

 the fruits and seeds ; while we find the products of assimilation of the Potato-plant 



Fig. 122.— a cells with cliloropliyll-corpuscles, from the FiG. 223.— Two filaments ot Spircffyi-a in conjugation ; 



leaves of a Moss {Funana kygrometrica). B isolated the band of chlorophyll containing groups of starch-grains, 



chlorophyll-corpuscles, a b with enclosed small starch-grains ; 

 <-rf« the same grown larger. *'*" a chlorophyll-corpuscle 

 dividing, y one swollen in water, s 'he same dissolved, the 

 starch alone remaining. 



to a large extent stored up in the tubers, and those of the Beet in the huge root 

 abounding in sugar. 



Having thus learned to understand the amount of work performed by chlo- 

 rophyll, first with reference to the external circumstances and then to the quantity, 

 we may now submit the question, what takes place in the chlorophyll-corpuscle itself 

 in these processes ? Here a distinction is to be made between the changes im- 

 mediately perceptible with the aid of the microscope and micro-chemical reactions, 

 and the chemical processes .which take place in the substance of the chlorophyll- 



' [ Sachs has since proved this to be the case. See Arbeiten des hot. Inst, in IViirzlnirg, B. Ill, 

 where experiments show that as much as 20-25 grams of starch per day may be formed by 

 I square metre of leaf-surface. An abstract of this paper appeared in 'Nature ' for April 10, 1884.] 



