407 



The fact that experiments in sterilized soil, as contrasted with those in 

 non-sterilized soil, resulted in much smaller amounts of yield, is ascribed 

 by Demoussy to the killing of the micro-organisms which, by their activity, 

 contribute to the decomposition of the carbon dioxid production. It is also 

 probable that the growth of plants close to the ground is favored by the 

 carbon dioxid constantly given off by the soil, since it has often been de- 

 termined that air at the surface of the soil contains more than three ten 

 thousandths carbon dioxid. 



In air in which the carbon dioxid has a tension five times above the 

 normal, a great many different plants increased about possibly 60 per cent, 

 more in weight than they did in ordinary air. These also blossomed earlier 

 and more abundantly^. 



If plants, which naturally behave differently according to species and 

 individuality, are no longer able to utilize the carbon dioxid given them, 

 their life functions must cease. Kosaroff- distinguishes between a specific- 

 ally injurious effect, and one due indirectly to the decrease of the partial 

 pressure, or rather, the removal of oxygen. As a result of the depression 

 of the transpiratory current, the plants wilt. Bohm^, like Saussure, ob- 

 served that germination was retarded, in that with an increase of carbon 

 dioxid, the roots and stems constantly became shorter and shorter. The 

 chlorophyll formation and assimilation were considerably decreased. 



Neither can geotropism be perceived in articulated plants (Gramineae 

 Commelinaceae, etc) in a carbon dioxid atmosphere, nor may a stimulus, 

 found in the air, initiate any bending*. 



Finally, when carbon dioxid begins to be excessive, the effect may first 

 be beneficial, then later gradually harmful. Reference should be made 

 here to the experimental results obtained by Brown and Farmer^. They 

 observed that, with an increased carbon dioxid content in the air, all the 

 parts containing chlorophyll became a darker green after 8 to 10 days, and 

 the starch content increased, but the internodes became short and thick, 

 the leaves rolled up even to the point of deformity, the flower buds dropped, 

 or their primordia were not formed. 



Such conditions as are given in the experiment need scarcely ever be 

 feared in practice. Such cases occur most frequently in hot beds where the 

 manure, needed to raise the temperature of the beds, sets free too much 

 carbon dioxid. This trouble may be overcome by proper ventilation, (even 

 on frosty days.) 



1 Demoussy, E., Sur la vegetation dans des atmospheres riches en acide car- 

 bonique. Compt. rend. CXXXIX, p. 883. 



2 Kosaroff, P., Die Wirkung der Kohlensaure auf den Wassertransport in 

 den Pflanzen. Bot. Centralbl. 1900, Vol. 83, p. 138. 



3 Sitzungsber. d. Wiener Acad. 1873 vom 24. Juli. 



4 Kohl, Die paratonischen Wachstumskriinimungen der Gelenkpflanzen. Bot. 

 Zeit. LVni, 1900, p. 1. 



5 Lioc. cit. 



