€0 SUMMAKY OF CUBRENT RESEARCHES RELATING TO 



normal) the curvatures vary with the strength of the curreut. In 

 every ease the curvature varies with the species. A weak current acting 

 for a prolonged period produces negative curvature ; very strong ones, 

 on the other hand, produce a positive curvature ; while S-shaped 

 curvatures are the result of prolonged, medium currents. The time of 

 influence required to produce any given ciu'vature varies inversely with 

 the strength of the current. There is no definite distinction between 

 the strength of currents required to produce positive and those required 

 to produce negative curvatures, for by alteration of the time of influence 

 the same current can produce either positive or negative curvatures. 

 The positive and negative curvatures differ in nature, the positive being 

 harmful in character, while the negative resembles that due to geotropic 

 stimulus. The S-shaped curvature represents the transition from 

 positive to negative. The author concludes that galvanotropism is a 

 special case of traumatropism. 



EflFect of Light and Temperature upon Chlorophyll Assimilation.* 

 TV. Lubimenko has experimented with numerous shade-loving plants 

 (ombrophiles), such as species of Abie.s, Firea, etc., and shade-avoiding 

 (ombrophobe), such as Fi/ii/s, Rohima, etc., with the ol)ject of deter- 

 mining the efl'ect of Ught and temperature upon photosynthesis. The 

 author finds that under the conditions which obtain when chemical 

 reaction is taking place in the interior of a living plant, light and heat 

 generally act similarly upon the energy of VO^ assimilation. For both 

 these factors there are optima of intensity, above which assimilatory 

 energy is weakened. The dimiimtion of assimilation, after these 

 optima are reached, is more strongly marked in ombrophiles tlian in 

 ombrophobes. 



Action of Light upon Transformation of Sugars.f — M. Lubi- 

 menko has also investigated the action of light upon the sugar absorption 

 of Finus Fi/iea, with the following results. In a weak liglit, the 

 seedlings transform the sugar absorljed l)y them, into a compound 

 analogous with saccharose. This transformation increases as the 

 intensity of light becomes greater, but reaches its maximum in a very 

 weak intensity, which is insufficient for the chlorophyll to decompose 

 €0^. In a stronger light, sugar assimilation decreases, but as the 

 chlorophyll is now able to decompose CO2, the dry weight of the plant 

 is again increased ; this last increase must be the result of reactions 

 unconnected with sugar assimilation. These results seem to point to a 

 new series of photochemical reactions, which take place in the plant-cell, 

 independently of chlorophyll assimilation. 



Rotation of Leaves of Marsilea.J — R. F. Griggs records some 

 observations on the diurnal rotation in leaves of Mars ilea vestita. The 

 rotation is remarkable, and is not due to movement or twisting of the 

 common petiole, but rather of the petiolules of the leaflets. 



* Comptes Rendus, cxliii. (1906) pp. 609-11. 



t Tom. cit., pp. 516-19 (1 fig.). 



X Ohio Naturalist, vi. (1906) pp. 554-5. 



