84 AERATION AND AIR-CONTENT. 



carbon dioxid between flowering plants and fungi. The first were 

 killed by long immersion in 20 to 30 per cent CO2, while the fungi 

 could not be entirely killed in any intensity. With the former the 

 growth stopped at 20 to 30 per cent, with the fungi at 40 to 80 per 

 cent. The optimum amount of CO2 for the growth of the higher 

 plants studied was about 0.5 per cent. Carbon dioxid in small 

 amounts acted as a stimulus, but in greater amounts as a poison. 



Nabokich (1903 : 272) combated the views of Wieler and of God- 

 lewski and Polzeniusz as to the suppression of growth in the absence 

 of oxygen. He found that hypocotyl of sunflower, 48 to 49 mm. 

 long, made an average growth of 6.3 mm. during 35 hours in pure 

 hydrogen, while another set gave an average of 4.8 mm. during a 

 36-hour culture. Seedhngs were also grown in a series of containers 

 of about 100 c.c. volume, with difl'erent amounts of oxygen for 20 

 hours with the results shown in table 25. 



In a later paper (1909 : 51), the same author table 25 



has given an extensive and unsympathetic ac- 

 count of the work of other investigators upon 

 growth in the absence of oxygen. The authors 

 considered were Borodin, Pfeffer, Wortmann, 

 Detmer, Moller, Wieler, Palladin, Pringsheim, 

 Clark, Correns, Chudiakow, Iwanowsky, Jodin, 

 Kuhne, Celakowsky, Ritter, Maze, Godlewski 

 and Polzeniusz, Polowzow, and Dude. In addi- 

 tion to extending his earlier studies of growth, 

 he found that shoots of Pisum exposed to oxygen- 

 free media for 53^ hours showed all the stages of 

 mitosis, just as in the control shoots, but that in 50-hour exposure, 

 all nuclei were in the resting-stage except those that had dissolved, 

 probably as a result of the death of the protoplasm. He concluded 

 that anaerobic growth in certain relations is completely identical 

 with normal aerobic growth. This is chiefly shown by the fact that 

 the development of plants in oxygen-free media takes place in accord- 

 ance with the usual rules, that the plants retain the abiUty to respond 

 to external stimuli, such as gravity, in the ordinary manner, and 

 that the growth of tissue results from the formation of cells by nor- 

 mal mitosis. On the contrary, other phenomena are in disagreement 

 with normal aerobic growth. These are the universal death of cells 

 in oxygen-free media, the peculiar course of the curve of growth 

 in different periods, and the specific dependence of growth upon the 

 temperature and upon the sugar solutions. 



Mitscherlich (1910 : 158) has studied the effect of increasing the 

 C02-content of the soil upon the production of oats, and finds that 

 it has no effect in increasing the harvest. He thinks that the 

 amount of CO2 in the soil derived from the roots and from the com- 

 position of humus is so great that the solubility of nutrients can not 



