262 ON THE ACTION OF LIGHT 



nature of the river sponge. Every one knows that when it 

 is necessary to blanch vegetables, they are carefully concealed 

 from the light ; and when plants are grown in a dark place, 

 they are of a delicate white, or yellowish- white, and perfectly 

 devoid (6) of their natural green colour ; but which, on their 

 being exposed to the light, soon becomes conspicuous, and 

 after a short time the plants obtain their usual green. (7) So 

 also, with most flowers and fruits, their colours are more or 

 less bright and vivid, according as they are exposed to or 

 concealed from the sun ; and I have sometimes noticed, that 

 purple grapes (the Black Hamhurgh, for instance), on being 

 gathered and placed for a few days out of the light, in a dark 

 closet, apparently lose somewhat of their deep and rich 

 colour. I would, therefore, suggest that this remarkable and 

 peculiar (8) property of light, which causes, as well as in- 

 creases, the colours upon the several parts of plants, might be 

 appropriately termed, the chromatic action of light. Whilst, 

 on the contrary, from this action upon the colours of ani- 

 mals, no such effect is known to occur ; for with them a very 

 powerful light, such alone as is communicated by the most 

 luminous rays of the sun, has merely the effect of darkening, 

 or, as it is more commonly called, tanning the skin, and 

 9iot of causing any distinctly bright or new colours to ap- 

 pear. (9) Neither does any similarity herein exist (as far as I 

 am aware) with regard to the lower animals, that more nearly 

 approximate to plants, as the Animal-Jiowers, or Actinice ; 

 because, from much acquaintance with some of these singular 

 creatures, both from having observed them in their native 

 localities among the rocks of our sea shores, and from having 

 often kept them alive in glasses, for the sake of attentively 

 examining their structure and habits, I have never noticed 

 any difference between the colours of those which inhabit 

 deep holes underneath the rocks (10) about low- water mark, 

 that are thickly covered with the dark sea- weeds (Fucus ser- 

 ratus, and F. vesiculosus chiefly), and so concealed from the 

 light, and of others which adhere upon the surface of the 

 rocks, and are well exposed to the solar rays. Nor have I 

 been able to ascertain that the green colour in the common 

 green fresh-water Polype [Hydra viridis, Lin.) is ever found 

 to vary, or to become more or less manifest, by admission to, or 

 exclusion from, the light. [11) But it would be superfluous to 

 add any further examples of the same kind. 



Some naturalists, even at the present day, are doubtful 

 respecting the real nature of the Spongilla, as well as of the 

 other SpongiadcB (if animals), or Spongiacece (if plants), 

 although the majority appear to decide in favour of their 



