260 Brown. — On the Germination and Growth of 
Farmer and Chandler (11)). 1 In the case of green plants, though Chapin 
considers carbon dioxide to act here mainly as a stimulant merely, the 
effect is complicated by its use for photosynthetic purposes, and on that 
account these results are scarcely relevant to the present investigation. 
Frankel (12) examined the effect of carbon dioxide on the growth of 
various micro-organisms on liquid or solid culture media. He found that 
whereas some organisms, e. g. the true beer yeasts, can grow as well in an 
atmosphere of 100 per cent. C0 2 as in air, the vast majority both of 
saprophytic and parasitic forms are inhibited by such treatment. He 
showed that this inhibition was due, to the actual presence of carbon 
dioxide and not to mere absence of oxygen, and that the effect was one 
of inhibition and not of killing, as the organisms subsequently grew 
normally when again placed in ordinary air. He also pointed out the 
marked variations in susceptibility of different individuals in the same 
culture (quite apart from spore forms), a feature which was also emphasized 
by Frankland (13). 
Lopriore (14), who gives a full account of the earlier literature, showed 
among other things that the germination of the spores of Mucor mucedo 
was slowed by the action of io per cent. C0 2 in the atmosphere, and that 
undiluted carbon dioxide, though producing total inhibition, did not kill 
the spores even after an exposure of three months. Sporangium formation 
was more readily suppressed than spore germination. Lopriore noted 
a tendency of the mycelium to form swollen cells under the carbon dioxide 
treatment. He also states that low percentages of C0 2 (i-io per cent.) 
accelerate the growth of pollen-tubes. 
According to Plummer (15) the ammonifying bacteria are very 
insensitive to the action of carbon dioxide, 6 o per cent, of this gas in the 
atmosphere having no appreciable effect on the rate of ammonification. 
Kidd (16), working with seeds of Brassica alba , found that the 
germination of the latter was inhibited by comparatively low concentrations 
(io per cent.) of carbon dioxide. The retarding effect of a given con- 
centration of carbon dioxide was dependent upon the pressure of oxygen 
present, being greater the lower the oxygen pressure. Kidd also describes 
acceleration of growth caused by a sufficiently low concentration of carbon 
dioxide. 
Oxygen . Out of the very voluminous literature dealing with the effect 
of oxygen pressure on plant growth, it is only necessary here to cite the 
work of Porodko (17), in which maximal and minimal concentrations of 
oxygen for a number of micro-organisms are given. From this work it 
appears that aerobic organisms are very insensitive to changes in oxygen 
pressure. Thus for Penicillium glaucum the maximum pressure at which 
1 It is, however, possible that some of the effects recorded may have been due to impurities in 
the carbon dioxide employed. 
