
1905. | Effect of Carbon Dioxide on Roots. 357 
It is not improbable that the dissociated substance is principally concerned 
in the causation of the physiological effects described above. The manifes- 
tation of these results may be due to the action of the H, or of the HCO; 
ions. (The possibility of direct action of H,CO3 being of the same order as 
that of the unchanged CO:.) It is hoped shortly to publish the results of 
experiments undertaken with a view to the elucidation of this at present 
obscure problem. | wo 
Whether the action take place by union with the protoplasm itself, or by 
combination with some metabolite, thereby putting this latter substance out 
of the field of physiological action, remains to be determined. 
It must be borne in mind that the external partial pressure of carbon 
dioxide aJone is known, whereas it is the partial pressure within the pea that 
determines the strength of solution and the amount of ionisation. It is true 
that the external partial pressure to a very considerable extent determines 
the internal pressure, but in addition to this is the carbon dioxide constantly 
evolved in respiration of the cells. At a certain stage the carbon dioxide 
penetrating from without, together with that evolved by the cells, will create 
an internal partial pressure equal to the external one. But as respiration 
proceeds the partial pressure within the pea will exceed that outside, and a 
slightly higher internal pressure will be maintained as long as respiration — 
continues. Hence, what has been determined by the above experiments is 
the partial pressure of carbon dioxide in the external atmosphere sufficient to 
produce during the time of experiment the optimum strength of solution in 
the cell sap. | 
LITERATURE. 
1. De Saussure. ‘Recherches chimiques sur la végétation,” Paris, 1804, in ‘Ostwald’s 
Klassikern.’ 
2. Bohm, Jos. “Sitzungsberichte der Wiener Akademie,” 1873. 
3. Montemartini. “Sulla influenza di atmosfere ricche di biossido di carbonio sopra lo 
sviluppo e la struttura delle foglie,” ‘ Atti del Istituto Botanico di Pavia,’ 1892. 
4. Chapin, P. ‘Einfluss der Kohlensaéure auf das Wachsthum. Flora,” 1902. 
5. Brown and Escombe. “The influence of varying amounts of Carbon dioxide in the 
air on the photosynthetic process of leaves and on the mode of growth of Plants,” 
‘Roy. Soc. Proc.,’ London, 1902. 
6. Farmer, J. B., and 8. E. Chandler. “On the influence of an excess of Carbon dioxide 
in the air on the form and internal structure of plants,” ‘ Roy. Soc. Proc.,’ London, 
1902. 
7. Ewart, A. “The Physics and Physiology of Protoplasmic Streaming,” London, 1903. 
8. Farmer, J. B., and A. D. Waller. “Observations on the action of Anesthetics on 
vegetable and animal Protoplasm,” ‘ Roy. Soc. Proc.,’ London, 1898. 
9. Brown and Escombe. “Static Diffusion of Gases and Liquids in relation to the 
assimilation of Carbon in Plants,” ‘ Phil. Trans.,’ B, 1900. 
