CHLOROPHYLL 



29 



If you examine the cells of the green leaf you will find in 

 their protoplasm small spherical discs, known as chloroplasts; 

 and the chlorophyll is confined to these chloroplasts and, as 

 a rule, is not diffused through the protoplasm, though there 

 are exceptions. In Spirogyra, a fresh-water alga, the chloro- 

 plast is in the form 

 of a spirally wound 

 band. Chlorophyll 

 consists of a mixture 

 of colouring matters, 

 the two most domi- 

 nant of which are 



D-rppn and the others ^.^"t' '-^"^^^^^^^F^'^yy^- c, tue s [mauy wo unu 

 green ana ine omers chloroplast; p.u., the protoplasm lining the cell; 



yellow. It IS not sol- w, the nucleus suspended by protoplasmic ropes; 

 uble in water or it V^ numerous small starch grains. (Darwin's 



1 J u J • ' 1 J Elements of Botany. ) 

 would be dissolved 



out in the sap; but it is soluble in alcohol and in certain 



other fluids. Now the most wonderful thing about chlorophyll 



is that in the sunlight it can build up the plant's simple food, 



carbon dioxide, COg, and water, HgO, into sugar and starch, 



setting free a certain amount of oxygen, which leaves the 



plant as an excretion. 



n. 



c. p. u. 



Fig. 7. A cell of Spirogyra. c, the spirally wound 



The Oxygen and Carbon Dioxide Cycle 



The first stage of the j^rocess is thought to be a chemical 

 compound called formaldehyde, and a method has quite 

 recently been discovered by which formaldehyde can be photo- 

 synthetically produced outside the plant's body. But as yet 

 formaldehyde has not been found in the cells of the leaf. If 

 it occurs it is only momentarily and is probably at once 

 converted into sugar (glucose). The soluble carbo-hydrates 

 (sugar, etc.) with certain simple salts build up a series of 

 elementary nitrogenous compounds know'n as amino-acids 

 and these by further synthesis lead to jjyoteins. Amino-acids 

 can be separated out from proteins and can be artificiall\' 

 made in the laboratory. By subjecting carbon dioxide and 

 water to rays of light of very short wave-length, far beyond 

 the violet end of the spectrum, formaldehyde has been pro- 



