150 M. Marc Micheli on some Recent 



enables the author to construct the curve of assimilation. 

 This curve, which is nearly parallel to the curve of luminous 

 intensity, attains its culminating point between the Fraunhofer 

 lines D and E. On the other hand it has nothing to do 

 with the curve of calorific intensity, which follows a totally 

 different course. 



Finally the author was led to confirm his results by data as 

 to the augmentation of weight acquired by plants under the 

 influence of the different regions of the spectrum. These data 

 are derived from unpublished experiments by Prof. Sachs ; their 

 author has ascertained that even in blue light there is an in- 

 crease of weight, which is certainly very slight, but greater 

 than it appears at the first glance, since we must take into 

 account the loss of solid material due to respiration. In yellow 

 light the increase of weight represented 35 per cent, of what 

 it would have been in white light. 



The study of the diffusion of gases in the interior of the 

 plant seems to be naturally connected with that of the con- 

 ditions under which assimilation is performed ; but although 

 the results of such researches belong to pure physiology, the 

 course by which we arrive at them, and the experiments and 

 apparatus employed, all belong rather to the domain of phy- 

 sics. The most difficult problems of molecular physics are 

 implicated in the questions which have to be solved. There- 

 fore we shall confine ourselves to indicating, en j^assantj a very 

 important and complete work upon this subject from the pen 

 of M. N. J. C. Milller*, still in course of publication in Prings- 

 heim's ' Jahrbiicher fiir wissenschaftliche Botanik.' We sliall 

 only say that the author adopts the idea that, in the normal 

 state of a membrane, the solid nuclei (formed of cellulose sub- 

 stance and mineral incrustations) and the liquid layers which 

 surround them (molecular theory of Ngegeli) always leave be- 

 tween them free spaces, actual pores. 



Before quitting the subject of the exchanges of gas between 

 plants and the circumambient atmosphere, we may mention 

 two other observations, due to French naturalists. 



M. van Tieghem f hfvs observed the well-known phenomenon 

 of aquatic plants which, although incapable of producing any 

 current of bubbles of gas under the influence of diffused light, 

 set them free in abundance as soon as they are struck by the 

 rays of the sun ; but what he has remarked that is new, is that 

 this effect does not cease immediately with the insolation. A 



* " Untersuchungen liber die Diffusion atmospharisclier Gase in tier 

 Pfianze," Prinp^sheini's Jahrb. vols. \i. & vii. 

 t Ann. des Sci. Nat. 5e ser. tome ix. p. 269. 



