266 ON THE ACTION OF LIGHT 



(7) I need not detail here the experiments by which 1 be- 

 came convinced of the truth of the before-mentioned curious 

 results. One case, indeed, did not occur to me to try ; but 

 which is thus related by Dr. Daubeny : — " Professor De Can- 

 dolle found that the leaves of plants placed in a cellar became 

 green on exposure to a strong light from lamps.'"' — (See 

 'Phil. Trans.,' 1835, p. 161.) Mr. N. B. Ward, F.L.S., has 

 also kindly informed me, that from very recent experiments, 

 he has ascertained that crocuses, grown in a dark situation, 

 and submitted for about six hours every evening to the full 

 influence of gas light, secreted in their leaves their usually 

 bright green colour, and that the flower of one specimen 

 received a pale hlue. Another case I have commenced, but 

 not as yet satisfactorily advanced; namely, how far the 

 greenness in the leaves and other parts of vegetables at first 

 grown in the light, is fugacious, and liable to lose its depth 

 of colour on being afterwards excluded from the light, and 

 confined to total darkness. 



(8) There can be no foundation, I think, for asserting that 

 heat, independent of light, possesses the like chromatic ac- 

 tion : because plants, when forced by artificial heat, but 

 deprived of light, are not invested with their green colour ; 

 and fruit, howsoever ripe it may be made by the high tem- 

 perature of a stove or hothouse, if concealed from the light 

 by many leaves, or in any other way, remains quite pale, and 

 never receives its proper and full tints. The same thing 

 likewise takes place with fruit, from which the light is exclu- 

 ded, when ripened by the heat of the sun. 



(9) With many animals which have variable fur or plumage, 

 heat and cold, but not light, are the principal causes of their 

 variations in colour. In support of these facts, consult my 

 paper on the changes in the colour of the fur in the ermine, 

 at p. 718, vol. 5, ' Magazine of Natural History ;' and for 

 Capt. Ross's very conclusive experiment on this subject, 

 refer to Professor Bell's * British Quadrupeds,' p. 153. 



(10) Notwithstanding that the Actinice are endowed with 

 the power of locomotion, I have watched some individuals 

 continue fixed in the same crevices of rocks for many suc- 

 cessive days, indeed, for a sufficient time to render any 

 change in their colours quite conspicuous. 



(11) M. Trembley tried to communicate to the hrown Polgpe 

 {Hydra fusca), a green tint. Not having any water insect 

 of that colour, he had recourse to the green variety of the 

 rose louse {Aphis ros(B ?) Several Polypes devoured some 

 of those green lice, and after th^y had digested them, they 

 received a faint colouring of green ; {vide Mempires pour 



