CHLOROPHYLL AND LIGHT INTENSITY. 379 



continuous spectrum is produced — violet, dark blue, light blue, green, yellow, 

 orange, and red. If the same sunbeam passes through a transparent but coloured 

 body, which may be either solid or fluid, whole groups of colour absent themselves 

 from the spectrum. Dark bands appear in the corresponding places, and we say 

 that the light in question has been absorbed by the coloured body. Now, if 

 chlorophyll has the property of absorbing those colours of the spectrum which are 

 not advantageous in the formation of organic substances from raw material, the 

 role of this chlorophyll cannot be too highly estimated. It must not be overlooked, 

 moreover, that many bodies have the capacity of absorbing light rays of shorter 

 wave-length, and, on the other hand, of giving out rays of greater wave-length. 

 It is precisely those pigments which are distributed in plants, again above all, 

 chlorophyll, which possesses this property called fluorescence; and we must 

 therefore also assign this significance to chlorophyll, that it can transform rays of 

 light which are useless in the synthesis of organic materials into those which show 

 the best possible action in this respect. If the fluorescing pigments of plants 

 (chlorophyll, anthocyanin, phycoerythrin) can transform the violet and blue rays 

 into yellow and red, it is to be supposed that their activity goes further, and that 

 they will be able to change rays of small wave-length and higher refrangibility into 

 rays which are found beyond the red, which are imperceptible to our eyes, and 

 which possess very great heat-giving powers, or, in other words, that they will be 

 able to transform light into heat. From all this it may be seen that the 

 significance of chlorophyll in the formation of organic materials would be three- 

 fold. First, a retention or extinction of those rays which might hinder the 

 formation of those compounds known by the name of carbohydrates; further, the 

 transformation of rays with short wave-length into those of longer wave-length, 

 which, according to experience, most favourably efiect the production of sugar and 

 starch; and, finally, the conversion of light into heat, and ultimately into latent 

 heat. 



CHLOROPHYLL -GEANULES AND THE GREEN TISSUE UNDER THE 

 INFLUENCE OF VARIOUS DEGREES OF ILLUMINATION. 



If it is beyond question that organic materials can only be formed from the 

 absorbed carbonic acid in the presence of chlorophyll, it is, on the other hand, equally 

 certain that the sun creates and works through these formative processes by its 

 rays, and thus, as the propelling force, becomes the fountain of all organic life. The 

 sun rises and sets, day follows night, and during the night the process just men- 

 tioned, upon which the existence of the living world depends, is interrupted. But 

 even in the daytime also, the strength of the sun is very unequal; it is one thing at 

 mid-day, when the source of light is in the zenith and the rays fall perpendicularly 

 on the earth, and quite another in the evening, as the illuminating orb sinks 

 below the horizon and the last rays spread almost horizontally over the surface. 

 Clearly it is anything but a matter of indifierence to the organs possessing a certain 



