156 VEGETABLE -PHYSIOLOGY 



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 

 alkalis, 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, 

 chlorophyll absorbs these particular rays of light which are 

 missing. 



