ACTION OF CHLOROPHYLL 441 



Chlorophyll is not soluble in water, nor can it be extracted with 

 acids or alkalies without alteration. 



A solution of chlorophyll in any of the liquids mentioned 

 shows the curious property* of fluorescence ; if regarded by 

 transmitted light it appears green, but if a strong solution is 

 looked at by reflected light it has a blood-red coloration. 



If a solution of chlorophyll is placed in the path of a beam 

 of light which is then allowed to fall upon a prism, the 

 resulting spectrum is found to be modified. Instead of showing 

 a continuous band in which all the colours are represented, it 

 is interrupted by seven vertical dark spaces. The rays which 

 in the absence of the solution of chlorophyll would have occupied 

 those spaces have no power to pass through it, or, in other words, 

 chlorophyll absorbs those particular rays of light which are 

 missing. 



In fig. 1186 is a representation of the spectrum, called from 

 the facts just narrated the absorption spectrum. The first band 

 on the left is the darkest, and is found to be in the red part of 

 the spectrum. The three bands on the right are broader, but 

 not so well defined. They cover nearly all the blue end. The 

 three thinner and lighter bands are in the green and yellow 

 parts of the spectrum. Chlorophyll therefore has the power of 

 absorbing a large amount of red rays, a good many blue and 

 violet ones, and a few of the green and yellow. The distinctness 

 with which the absorbtion bands are seen will depend upon the 

 strength of the solution, the red and blue being, however, always 

 prominent. 



Careful chemical experiments have proved that chlorophyll 

 is a single pigment, and not a mixture of two as has often been 

 stated. It is, however, very easily decomposed, and the products 

 of its decomposition are generally found with it in the chloro- 

 plastid. One of these, XanfJiojjhyU, which is of a bright yellow 

 colour, is always extracted with the chlorophyll by alcohol. It 

 can be separated by appropriate treatment. 



Chlorophyll is formed in the chloroplastids only when they 

 are exposed to light, except in one or two rare cases. When a 

 plant is grown from a seed or a tuber in the dark, the resulting 

 stem and leaves are not green, but of a peculiar yellowish-white 

 appearance. Nor can it be developed in the absence of a suit- 

 able temperature. Its formation has been found to depend 

 upon the presence of iron in the plant, but the exact relation of 

 the iron to the pigment is not known ; it does not appear to enter 

 into the composition of the latter. 



