CHLOROPHYLL 195 



But an impure solution of chlorophyll may be obtained by 

 extracting the leaves by the aid of methylated spirits. The 

 leaves in time become whitish in colour, and the solution 

 becomes coloured. The solution is green in colour when 

 we look through it ; whereas it appears to be blood-red if 

 we inspect it when placed before a dark background. Light 

 decomposes the chlorophyll in the alcohol -solution, also in 

 plucked leaves themselves. This is all the more curious 

 because chlorophyll does not form in flowering plants unless 

 the latter be exposed to the light. A plant grown in darkness 

 has whitish or yellowish leaves. Bringing this bleached plant 

 into the light, the leaves soon assume a green colour ; light is 

 essential to the formation of chlorophyll. If the bleached 

 plant be killed before being exposed to the light it will not 

 produce chlorophyll ; the plant must be living if it is to make 

 chlorophyll. Again, if a germinating seed be supplied with the 

 solution mentioned on page 191, excepting that the iron be 

 omitted, the plant grows for a time, but is yellow. If we now 

 supply the iron, it becomes green. Therefore iroti is required 

 for the formation of chlorophyll. Finally, a certain degree of 

 warmth is essential for the manufacture of chlorophyll. 

 Probably the autumn tints of leaves are partially associated 

 with the decomposition of the chlorophyll under the influence 

 of light and the slowness of the production of new chlorophyll 

 because of the low temperature prevailing. 



