THE CHLOBOPHYLL APPAKATUS 147 



pigment which is in these bodies is of a fatty nature, and 

 is probably some kind of oil. Alcohol, chloroform, ether, 

 benzol, and a few other liquids can extract the chlorophyll 

 from the plastids and leave them colourless. The pigment 

 can be obtained from them also by treatment with dilute 

 alkalies, such as potash and soda. By whatever solvent it 

 is extracted, however, it appears to undergo decomposition, 

 so that the solution does not yield it up in the form in 

 which it exists in the vegetable cell. 



A solution of chlorophyll in alcohol or chloroform shows 

 the curious property of fluorescence ; if regarded by trans- 

 mitted light it appears green, whatever may be the degree 

 of concentration of the solution ; if a strong solution is 

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



When a beam of white light is allowed to pass through 



a prism, and is then made to impinge upon a screen of white 



paper, it gives the appearance of a band in which all the 



colours are represented in the following order : red, 



orange, yellow, green, blue, indigo, and violet. This is due 



to the different degrees in which the rays which produce 



the sensations of those colours are bent or deflected by 



the prism. This coloured band is called the spectrum of 



white light. In order to get it exhibited to the greatest 



advantage, it is best to admit the beam of light to the 



prism through a narrow slit. The spectrum may then be 



regarded as a succession of images of the slit, each ray 



giving its own image of the aperture and producing that 



image in its appropriate colour. If a solution of chlorophyll 



is placed in the path of the beam before it reaches the slit, 



the resulting spectrum is found to be considerably 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 would have occupied these 



spaces in the absence of the solution of chlorophyll have no 



power to pass through the latter, and consequently their 



images of the slit are represented by dark lines, which 



together constitute the black bands. In other words, 



10* 



