190 INTERNATIONAL BOTANICAL CONGRESS. 
of oxygen by leaves, and upon the production of the green colouring- 
matter, have only confirmed the discoveries made in 1836, without 
either prism or heliostat, by Professor Daubeny,* from which it ap- 
pears the most luminous rays have the most power, next to them the 
hottest rays, and lastly those called chemical. 
Dr. Gardner, in 1843, Mr. Draper immediately after, and Dr. C. 
M. Guillemin in 1857, corroborated by means of the prism and the 
heliostat the discovery of Dr. Daubeny, which negatived the opinions 
prevalent since the time of Senebier and Tessier, and which were the 
result of erroneous 1 experiments. It was difficult to believe that the 
most refrangible rays,—violet for instance, which acts the most on 
metallic bodies,—as in photometrical operations, should be precisely 
those which have least effect in decomposing the carbonic acid gas in 
plants, and have the least effect over the green matter in leaves. Not- 
withstanding the confirmation of all the experiments made by Dr. 
Daubeny, when repeated by numerous physicists and by more accurate 
methods, the old opinions, appearing more probable, still influenced 
many minds,§ till Mr. Julius Sachs, in a series of very important ex- 
periments again affirmed the truth.|| It is really the yellow and orange 
Tays that have the most power, and the blue and violet rays the least, 
in the phenomena of vegetable chemistry ; contrary to that which 
occurs in mineral ehemistry, at least in the case of chloride of silver. 
The least Ee rays, such as orange and yellow, have also the 
Univ. de Genève, dae 1844; Die, Edinb. Phil. Mag. "3 
844, extract ib. 1844, vol. liv. ; ; Guillemin in (C. M.), Ann. Sc. Nat. 1857, in 
4, vol. vii. p. 154. 
——À Mém. Phys pe Chim., ii. p. 69; Tessier, — eor ye € 
Gilby, Ann. de Chimie, 1821, vol. xvii. ; Succo cow, ‘Com e Luc 
Effectibus is Chenicis Ato, Jena, An p. 61 ; Zantedeschi, cited E je eed 
Compt. Rend. Acad. Sc. 1 1, p. 
$t Asa T of the duc of the old. opinion, I will quote a phrase of 
n conseque i 
et rays are PT he utmost importance to the organic world." I do not 
know whether the author had in view an influence of the chemical rays over 
e d . S 
animal om; but, according ertain pa: Mr. Sachs, I 
doubt if they have more power over animals than they bave over p 
sides, Profe not concern lf with these questions, he was 
content to explain admirably the physical nature of the various rays. 
zo» The of Mr. Sachs fi: the ‘ Botanische Zeitung ;’ 
they are collected and condensed in the remarkable dco pe * Handbuch 
der Ph oe Botanik,’ vol. iv., Leipzig, 1865, pp 
