132 Notes on Recent Physiological Literature. 
Another explanation as to their function might he that they 
are water-storing elements, but this does not seem probable in a 
plant of the habit of Equisctiwi. The eosin experiment also showed 
that they were used in conduction. 
NOTES ON RECENT PHYSIOLOGICAL LITERATURE. 
I.—The Chemistry of Photo-synthesis. 
H. Euler. Zur Iventniss der Assimilationsvorgiinge I., Ber. d. deut. chem. 
Gesell. XXXVII., p. 3411, 1904. 
F. Usher and J. Priestley. A study of the mechanism of Carbon Assimilation 
in Green Plants. Proc. Roy. Soc., B Vol. 77, p. 369, Jan. 1906. 
R. Meldola. The Living Organism as a Chemical Agency : a Review of Some 
of the Problems of Photo synthesis by Growing Plants. Presidential 
Address to the Chemical Society, Jour, of Chem. Soc., April, 1906. 
| ^HE object of this short notice is to direct the attention of 
readers to recent papers on the chemical mechanism of C0 2 - 
assimilation. The early view which regarded protoplasm as an 
enormous molecule which, in assimilation, took up C0 2 directly, on 
the one hand and split off sugar on the other hand, has given place 
to the newer view, so much more hopeful for investigation, which 
holds that, in such functions as respiration and assimilation, we 
have to deal with a system of comparatively simple changes 
occurring in sequence, and that if we are only clever enough we 
shall be able to separate these stages. 
Von Baeyer in 1870 first suggested that production of form¬ 
aldehyde was an important stage in photo-synthesis, forming a sort 
of turning point between the reduction-processes that formed it 
from aqueous carbonic acid and the “condensation’’-processes that 
caused it to be built up into sugar and starch. 
In 1877 Erlenmcyer indicated that formic acid would probably 
be the intermediate stage in the reduction-process. 
Since that time a number of isolated experiments have been 
made on the reduction of C0 2 by light, in vitro as well as in the 
plant, but systematic critical investigation has only been taken up 
in the last two or three years. Investigation has been directed to 
four points, (i.) Does formaldehyde really occur free in the green 
assimilating leaf? (ii.) Can CO a be reduced by light in vitro in 
any way that will help to elucidate the process in the cell ? (iii.) 
