342 THE LIFE OF THE PLANT 



been absorbed by its substance. We can perform this experi- 

 ment more exactly still. Since the colour of the plant 

 depends on the chlorophyll, we can study the absorption of 

 light by the chlorophyll itself. Chlorophyll can be extracted 

 from leaves by means of spirit. We aU know that any kind of 

 infusion of leaves acquires a splendid green colour, which is 

 the colour of the chlorophyll. Therefore instead of nearly 

 opaque leaves we can use for our experiment a nearly transparent 

 chlorophyll solution. We fill a glass with this solution and place 

 it in the path of the sunlight, and then proceed to analyse with 

 a prism the light we thus obtain. This is the kind of spectrum 

 we get. The extreme red rays (from A to B, fig. 82) will have 

 passed through unabsorbed ; whereas in place of the brightest 

 red, the orange and part of the yeUow rays, the spectrum will 

 have a black band (fig. 82 from B to D) ;^ the green rays (between 

 D and a little to the right of b) will not be absorbed, and will 

 give a green band in the spectrum ; the blue and violet rays will 

 be likewise absorbed. Hence, instead of all the seven colours 

 the spectrum of chlorophyll wiU show only two coloured bands : 

 a dark red and a bright green, with a black space between them. 

 Hence we conclude that the green colour of a plant is not pure, 

 but a mixture of green and red. This can be easily proved by 

 a curious experiment. The commonest blue glass absorbs 

 green rays and lets through some red rays. It foUows that if 

 we look at green vegetation through a piece of this glass it wiU 

 arrest green rays on their way to our eyes, and let through only 

 red rays. German opticians have taken advantage of this fact, 

 and offered the public a rather amusing instrument called the 

 erithro-phyfoscope, which is simply a kind of blue spectacles, but 

 the moment you put them on the whole world changes its aspect. 

 A fantastic landscape with coral woods and meadows unrolls 

 itself under a deep blue sky. It might be useful to draw the 

 attention of some artists to this fact who are in the habit of 

 colouring their landscapes with that malachite green colour, 



' Fig. 82 represents a photograph of the absorption spectrum of chloro- 

 phyll. The blackest part lies within the red part of the spectrum. The 

 process of photographing the spectra has presented great difficulties, 

 even down to our own day. In the summer of 1893 I succeeded in 

 obtaining satisfactory photographs, which were demonstrated at a con- 

 gress of naturalists and physicians at Moscow in January 1894. The 

 letters mark the so-called Fraunhofer lines of the spectrum of the sun. 



