70 THE INFLUENCE OF INANIMATE SUEEOUNDINGS. 



CHAPTER III. 



THE INFLUENCE OF LIGHT. 



It has been poetically said that the plants and trees of our time 

 are the incorporate sunbeams of to-day, and that coal contains 

 the sunshine of long past epochs, divided from the present by 

 millions of years ; and the saying is to a great extent true, as 

 everyone knows, for the greater proportion of vegetable organ- 

 isms depend entirely for life and growth on the direct influence 

 of light. It is equally well known that animals are to a certain 

 extent independent of this influence. At the same time even 

 they are open to it, and the question might even be suggested : 

 Whether animals are not in fact at least as dependent as 

 plants on the direct influence of light, even though the nature 

 of their relations may be altogether difierent 1 In discussing 

 this point we will distinguish between the heat-giving rays and 

 the light-giving rays, even when these are in the most intimate 

 combination ; and we are justified in doing this, since we know 

 that these two modes of motion act upon living organisms in 

 difierent and often antagonistic ways. 



The difference between animals and p'ants. — If we except 

 the lowest organisms, the relations between light and the organ- 

 ism ssem to be maintained by two very dissimilar organic 

 structures— by the eye in the animal, and by the chlorophyll 

 bodies in plants. These, nevertheless, have been occasionally 

 compared."' Each organ would seem to preclude the other. 

 It is true we know of some highly organised animals that have 

 no eyes, and true plants which are devoid of chlorophyll ; but 

 plants never have eyes at all, and such animals contain no 



