ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 75 



In reference to the relation between intensity of light, growth, and 

 heliotropism, the following are Wiesner's conclusions : — (1) As the 

 intensity of light decreases, the growth of the internodes gradually 

 accelerates, if strong heliotropism has been induced by the maximum 

 light-intensity. (2) If the maximum intensity of light is too great to 

 induce obvious heliotropism, the increments rise, with the decreasing 

 illumination, to a certain limit ; a continuous increase of the length 

 of the internodes then again taking place. 



In opposition to the popular \iew, negatively heliotropic roots 

 grow more and not less rapidly in the dark ; this conclusion being 

 confirmed by F. Darwin, and very simply by the concm'rence of 

 positively and negatively heliotropic elements in the same organ. 



The paper concludes with the record of a great variety of observa- 

 tions on different organs. 



Influence of Light on Germination and Respiration * — 

 M. Pauchon states, as the result of a series of observations, that light 

 always promotes the absorption of oxygen by germinating seeds, the 

 quantity of oxygen absorbed in the light being from j to ^ greater 

 than in the dark, and exhibiting a gradual proportional variation. A 

 secondary action of light was observed, lasting for several hours, a 

 portion of the daylight being absorbed by the seed, and consumed 

 during the night. The difference in the amount of oxygen absorbed 

 in the light and in the dark is greater in winter than in summer, 

 showing that light acts more energetically at a low than at a high 

 temperature. 



These facts seem to explain the transformation of legumin into 

 asparagin. Asparagin, the form in which the reserve albuminoid sub- 

 stances are transported in the germination of the Leguminoste, only 

 disappears when the plant is exposed to the light, and remains in 

 those cells which continue dark. Asparagin contains less carbon and 

 hydrogen and more oxygen than legumin and the other proteids ; and 

 its transformation into legumin is thus effected in light which acce- 

 lerates the absorption of oxygen. 



Effect of the Intensity of Light on the Decomposition of Car- 

 bonic Acid by Plants. f—M. Famintzin has carried out a number of 

 experiments for the purpose of deciding the question whether there 

 is an optimum of light-intensity, an increase above which is unfavour- 

 able to the decomposition of carbonic acid. These experiments were 

 divided into two sets. 



1. Experiments in sunshine in a mixture of air and CO2, and then 

 in water containing CO2. — The sunshine was in some cases allowed 

 to fall direct on the object, in others it was moderated by one or 

 more thicknesses of paper. The result was that in a large number of 

 plants an optimum of light-intensity was established for the decom- 

 position of CO2. Above this there was no increase in the quantity 



* Oomptes Kendus, xci. (1880) pp. 692-4 and S64-6; and Ann Sci Nat 

 (Bot.), X. (1880) pp. 81-192. 



t Bull. Acad. Imp. Sci. St. Petersburg, xxvi. (18S0) pp. 296-314 • and Ann 

 Sci. Nat. (Bot.), x. (1880) pp. 67-80. 



