NOTES AND MEMORANDA. 139 



manner. Blue comes next, and then yellow and white, which are 

 nearly equal in their effects. 



(3) Darkness does not prevent development, but, contrary to the 

 results of MM. Higginbottom and MacDonnell, does retard it. 



(4) Eed and green light seem to be hurtful, as the complete 

 development of the eggs placed in these colours could not be 

 obtained. 



(5) Tadpoles subjected to the same conditions and deprived of 

 food died sensibly sooner in violet and blue light than in the others — 

 they consumed their food store more rapidly. 



(6) The mortality seemed to be greater in coloured light than in 

 white light. Nevertheless, as the results have not always agreed on 

 this point, it would be premature to consider this as positively 

 proved. 



2. Plants. — In 1869 M. P. Bert showed * that certain plants placed 

 under green glass soon died. He thought the explanation was to be 

 found in the green colour of the leaves — to allow none but gi-een light 

 to reach them was to give them what they rejected as useless. Eeflect- 

 ing that these leaves, under a great thickness, appeared red, he 

 thought the plants would die also behind red glass, but was surjirised 

 to see that they did not. 



This apparent contradiction led him to undertake a fm-ther ex- 

 amination.! 



If green and red glasses are examined through the spectroscope 

 by diflfused sunlight, we see that the red glass intercepts the yellow 

 and all the most refrangible part of the spectrum, only allowing the 

 orange and the red to pass ; while the green glass intercepts about 

 three-quarters of the red, starting from the left hand. 



The first maintains life, the second kills, and therefore the 

 necessary part of the spectrum is found in this red which the green 

 glass absorbs. 



To further determine whether this property is to be attributed to 

 the whole intercepted extent of the red, he compared a solution of 

 chlorophyll, with the gi'een glass, and saw that the part of the red which 

 it absorbed, extended, from left to right, as far as the first absorption 

 band characteristic of chlorophyll (included between the lines B and 

 C), and concluded that it was the part of the spectrum corresponding 

 to this band, which, absorbed by the leaf, was indispensable to its 

 life. 



Further experimenting, he found that plants, lighted by a good 

 diflfused light, and surrounded with vessels with parallel glass sides 

 containing an alcoholic solution of chlorophyll very frequently 

 renewed, immediately ceased growing, and very soon died : this 

 solution, which was very weak and in a very thin layer, intercepted 

 hardly any but the characteristic parts of the red. 



The indispensable part of white light is consequently there, where, 

 moreover, M. Timiriazeff J has recently found the maximum of re- 



* ' Comptes Rendus,' 14tli February, 1870. 

 t Ibid., vol. Ixxxvii. (187S) p. 695. 

 i Ibid. Sitting of 28th May, 1877. 



