82 AERATION AND AIR-CONTENT. 



that in normal air. In the case of Helianthus, no growth occurred 

 under entire exclusion of oxygen, and it ceased as soon as the oxygen 

 was excluded. Growth began again when the plants were placed in 

 atmospheric air, if they had not been without oxygen for too long a 

 time. Continued exposure to an oxygen-free medium worked serious 

 injury in most cases to the plant. Helianthus suffered exposure for 

 24 hours without damage, and grew vigorously when brought again 

 into atmospheric air. Vicia faba, on the contrary, suffered so after 

 22 hours that the plants blackened when placed in atmospheric air, 

 and Cucurbita died on the second day after being returned to it. 



Moller (1884) repeated Detmer's experiments with N 2 O, using 

 seedlings of Vicia faba, and found that no growth occurred, though 

 the seedlings suffered no damage in the 48-hour exposure. 



Palladin (1886) exposed seedlings of Vicia faba for 20 hours to 

 hydrogen and was entirely unable to find any growth, in contrast to 

 the behavior in air. 



Jentys (1888 : 452) stated that, with a single exception, in no case 

 was a complete stoppage of growth observed under greater oxygen- 

 pressure, but in all there was more or less marked reduction. Under 

 approximately equal periods of exposure, the reduction of the growth 

 of the stem parts was the greater the higher the pressure. He pointed 

 out that these results were in opposition to those of Bert, but ex- 

 plained this by the fact that Bert's experiments lasted 4 days in con- 

 trast to 4 hours. Raising the partial pressure of oxygen to one 

 atmosphere was decidedly favorable to the growth of seedlings of 

 Raphanus, Sinapis, and Brassica, but without any influence upon 

 the growth of Vicia, Helianthus, and Pisum. Sinapis and Raphanus 

 were found to grow better in pure oxygen, but more poorly in com- 

 pressed air, while indifferent gases, such as hydrogen and nitrogen, 

 worked unfavorably under increased pressure, as did also the re- 

 duction of the air-pressure below the normal. Peas and other 

 plants grew in air richer in oxygen just as well as in ordinary air. 



Montemartini (1892) observed that seedlings of spinach grew best 

 in 4 per cent CO 2 , less well in 7 per cent, and poorly in 22 per cent. 

 Those of Tropaeolum grew vigorously in 4 per cent, poorly in 7 per 

 cent, and perished in 22 per cent. The roots of peas grew slightly 

 better in 4 per cent C0 2 than in normal culture, while growth was 

 considerably retarded at 7 per cent and reduced more than half at 

 22 per cent. The higher amounts of carbon dioxid called forth 

 striking modifications in leaf-structure. The thickness of the pali- 

 sade increased in relation to the sponge parenchyma; its intercellular 

 spaces were smaller and the cells narrower. 



Jentys (1892 : 306) cultivated beans, wheat, rye, and lupines in 

 glass jars under the influence of varying amounts of C0 2 , namely, 

 4, 5, 8, and 12 per cent. The action of such mixtures was less in- 

 jurious than would be assumed from Bohm's results. In periods of 



