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Notices of Books and Papers. 
and the state of inanition was induced. In most cases the evolution of 
oxygen by the cell, as determined by the Bacterium-method, ceased 
much sooner than the rotation ; but in many instances the converse 
was the case. 
The bearing of these facts upon the relation between the process of 
assimilation and the supply of free oxygen is obvious. It is clearly 
proved by these observations, assuming the soundness of the methods, 
that this process of assimilation can only be carried on when the pro- 
toplasm is adequately supplied with free oxygen. In this conclusion 
Professor Pringsheim agrees with de Saussure 1 , but differs from Bous- 
singault 2 , who came to the conclusion that the absorption and decom- 
position of carbon dioxide by leaves is quite independent of free 
oxygen. The discrepancy between the results of Boussingault and of 
Pringsheim appears to be easily explicable in favour of the latter. It 
does not appear that, in Boussingault’ s experiments, there was any 
provision for a continuous current of the irrespirable gas or mixture of 
gases such as there was in those of Pringsheim. Hence, in the 
former, the oxygen gradually accumulated in the receiver, and 
consequently their value is vitiated. 
Professor Pringsheim draws from these facts the further conclusion 
that, in the process of assimilation of carbon, no oxygen is set free in the 
interior of the cell, but that a substance is formed in the cell which 
escapes by osmosis, and undergoes decomposition at the surface, free 
oxygen being one of the products. He argues that if free oxygen were 
evolved in the interior of the cell, it would be impossible for the arrest of 
rotation and the condition of inanition to supervene whilst the cell is 
exposed to light in an atmosphere containing carbon dioxide ; and, on 
the strength of this argument, he indulges in some severe strictures on 
the ‘ gas-analytical ’ method by means of which most of the existing 
knowledge of the process of assimilation of carbon from carbon 
dioxide has been obtained. He urges that the decomposition of car- 
bon dioxide and the evolution of oxygen are two distinct processes, as 
distinct as the absorption of oxygen and the evolution of carbon 
1 ‘ Nous venons de reconnaitre que le gaz acide carbonique ajoute artificielle- 
ment dans de tres petites proportions a l’atmosphere des plantes, est utile a leur 
vegetation au soleil ; mais il n’exerce cette action bienfaisante qu’autant que cette 
atmosphere contient du gaz oxygene libre.’ (De Saussure, Recherches Chimiques, 
1804, p. 33.) 
2 Boussingault, Etudes sur les fonctions des feuilles, Comptes Rendus, lx, 
p. 862, 1865 ; also, Agronomie, Chimie Agricole, &c., iv, 1868, pp. 301-2. 
