942 



SCIENCE. 



[X. S. Vol. XXI. Xo. 547. 



or other delicate methods, recently sug- 

 gested, for it is of considerable interest to 

 determine the relation of the photosynthetic 

 activity to such agents as compared with 

 other activities. 



Recently the effects of temperature on 

 photosynthesis have been carefully worked 

 out by Miss Matthaei. She states that the 

 curve of synthetic activity rises with in- 

 creased temperature, that it is in general 

 convex to the temperature abscissas and 

 somewhat similar to the curve of relation 

 between temperature and respiration. 

 There is a certain maximum for each tem- 

 perature. It has also been ascertained that 

 there is a certain economic light intensity 

 beyond which there is no increased photo- 

 synthetic activity, and doubtless only in- 

 jury. This is of special interest in connec- 

 tion with some recent work by Weis. Rec- 

 ognizing the fact that plants are of very 

 different types Avith relation to their light 

 requirements, he has sought to get an ex- 

 pression of their assimilatory energy. He 

 finds that (EnotJiera hiennis, a well-marked 

 sun plant, fixes under favorable conditions 

 of temperature, and in direct sunlight, 

 about three times as much CO, as in diffuse 

 light (light of one sixtieth to one ninetieth 

 this intensity). On the other hand, Poly- 

 podimn vnlgare assimilates in diffuse light 

 somewhat more energetically than in direct, 

 while Marchantia polymorpha occupies a 

 position intermediate. This will be wel- 

 comed by physiologists as a field for whole- 

 some ecological study, for an extension of 

 such investigations to an analysis of plant 

 associations with relation to the light factor 

 may yield profitable results. 



In 1901, Freidel made the surprising re- 

 port of success in securing outside of the 

 living plant a gas exchange similar to the 

 photosynthetic action of chlorophyll. He 

 was later unable to confirm his previous 

 conclusions, nor were the subsequent results 



of ]\Iacchiata and Herzog concordant. Re- 

 cently, Molisch has employed upon this 

 problem the photobacterial method of 

 Beijernick. He finds that the expressed 

 sap of certain plants may for a time main- 

 tain photosynthetic activity, but since usu- 

 ally the sap loses this power when filtered 

 through a Chamberlain filter, it is believed 

 to be due to the presence of living plasmatic 

 particles. Nevertheless, it is claimed that 

 an exchange of gases characteristic of 

 photosynthesis may proceed in a solution 

 of the leaves of Lamium album dried crisp 

 at 35° C. and then 'rubbed up' in water 

 and filtered. The observation demands 

 much further study, for it must be remem- 

 bered that the test is by means of the liber- 

 ation of oxygen, and Ewart has shown that 

 some bacterial pigments may have the 

 power of evolving oxygen. In the last- 

 named case the gas evolved appears to be, 

 as he states, 'occluded oxygen absorbed 

 from the air by the pigment substance ex- 

 creted by the bacteria.' 



It can not be stated at the present time, 

 however, as was assumed from Freidel 's 

 first work, that there is any enzyme con- 

 cerned in the photosynthetic activity. 



To a large extent the problems involved 

 in a study of the assimilation of nitrogen 

 are limited by the very imperfect chemical 

 knowledge of nitrogenous products, and 

 may not, therefore, be very clearly defined. 

 Practically, the whole question of the for- 

 mation of amides, proteids or other nitrog- 

 enous compounds in plants remains in ob- 

 scurity. It is known that these are formed 

 in both non-chlorophjdlous and chlorophyl- 

 lous plants and that while in the former it 

 may proceed in darkness, in the latter, light 

 is apparently required for the most vigor- 

 ous synthesis. In the latter case it may 

 seem to suggest that there is need of the 

 active cooperation of the chlorophyll ap- 

 paratus; but here again the influence may 



