II 



LIVING MATTEE 



59 



experiment being carried out in a glass jar (as shown in Fig. 14), 



the plant, under the influence of light, will develop normally, 



flower, and bear fruit. If the iron sulphate 



is wanting in the solution, the plant may 



live for some time, but its leaves will be 



colourless, and under the microscope show- 

 absence of chlorophyll; if the other salts 



are wanting, the plant will not germinate, 



or perishes as soon as it develops. 



This experiment proves that all the 



carbon assimilated by the plant is derived 



from the carbonic acid of the air the 



grand discovery of Ingenhousz ; further, it 



shows that the assimilation of carbon is 



conditioned by chlorophyll, the molecules 



of which contain iron ; lastly, the assimila- 

 tion of nitrogen is due to the reduction 



of nitrates, and the assimilation of sulphur 



and phosphorus to the reduction of sulphates 



and phosphates. 



The intimate processes by which the 



plant succeeds, by the assimilation of all 



these elements, in synthetically forming 



organic substances are for the most part 

 unknown. Thanks, 

 however, to the work of 

 Sachs, we know some- 

 thing of the process of 

 starch formation in the 



green parts, which may be taken as the starting- 

 point for all other synthetic processes in plants. 

 In the adult cell, chlorophyll is contained within 

 special ellipsoidal corpuscles known as chloro- 

 plasts, which are for the most part found in 

 ift-3 great numbers heaped against the parietal proto- 

 W~T plasm (Fig. 15). After a green plant has been 

 exposed for a few minutes to full sunlight, 

 starch granules are seen to appear in the middle 

 or edge of the chloroplasts, which gradually 

 increase in size until their volume exceeds that 

 of the chloroplasts. During the night, when 

 starch formation is suspended, this accumula- 

 tion is dissolved by the action of diastatic fer- 

 ments, and conveyed under the form of sugar 



to the parts in which it can be utilised as food material. 



Starch represents the principal nutritive reserve material that 



accumulates in a solid form in the plant cells in which it is formed. 



;. 14. Zra mais in culture 

 solution. Mg., grain of maize ; 

 .S'7!., Sachs' nutrient solu- 

 tion ; *, cork to support plant 

 in vertical position. 



FIG. 15. Two leaf-cells of 

 Funaria hygrometrica. 

 cl, chloroblasts ; n, 

 nucleus. Magnification, 

 300 diameters. 



