RESPIRATION AND OXYGEN. 79 



to produce delay. Bernard obtained no germination with cress in 

 16 per cent C0 2 , while Linossier concluded that it was merely delayed 

 at percentages up to 19, and completely suppressed only at much 

 higher ones. Jodin observed that 7 per cent affected the germina- 

 tion of peas but little, but that it occurred only incompletely at 13 

 per cent. The explanation of this wide variation apparently has 

 been furnished in part by Kidd, who finds that germination is in- 

 hibited by 2 to 4 per cent of carbon dioxid at 3 C., while 25 to 30 

 per cent was required to bring it about at 20 C. Even more sig- 

 nificant differences in response are occasioned by the use of different 

 species. Huber and Senebier early showed that peas, beans, lentils, 

 and wheat would germinate under water, though the seeds of most 

 species would not, and Bohm found similar differences in germination 

 in pure oxygen. Bert observed that the germination of starchy 

 seeds suffered more from high oxygen-pressure than that of oily 

 ones, and Jodin noted that peas were more susceptible to C0 2 than 



cress seeds. 



GROWTH. 



Early researches. While Scheele (1777) thought that plants could 

 not develop well in pure oxygen, and Ingenhousz (1786) found that 

 seedlings thrived better in it, Saussure (1804) was the first to make a 

 study of growth under anaerobic conditions. In pure oxygen, pea 

 plants in the shade were found to gain only half the weight that they 

 did in ordinary air, while in the light the gain was practically the 

 same in both cases. Plants without green parts were unable to 

 grow in pure nitrogen, nor were seeds able to germinate in it, but 

 decomposed quickly, as shown by seeds of pea, cress, and Polygonum 

 amphibium. Buds of Populus nigra and Salix alba, which were 

 ready to open, were unable to develop further in nitrogen, even in the 

 sunshine, but decomposed at the end of 15 days. Buds of roses, lilies, 

 and violets about to open were unable to develop in pure nitrogen. 

 Opuntia in pure nitrogen died in the shade in 6 days; in sunshine, it 

 survived for 3 months, but with great difficulty. Some pea plants 

 were able to resist the effect of nitrogen for 4 to 5 days. Such marsh- 

 plants as Lyihrum salicaria, Epilobium hirsutum, molle, and mon- 

 tanum, and Polygonum persicaria grew as well in nitrogen in weak 

 light as they did in ordinary air. Plants of pea, bean, and kidney- 

 bean died in 3 days in a vacuum, either in sun or shade, while fleshy 

 plants, such as Opuntia, lived for a month in the sun. The marsh- 

 plants mentioned above grew as readily in vacua as in ordinary air, 

 but this was considered to be due to the large amount of oxygen 

 contained in their tissues. It was concluded that plants can survive 

 or grow in vacua only by the aid of the oxygen evolved from their 

 green parts. Both seeds and roots died in a vacuum, woody plants 

 could not open their leaf-buds in it, and flower-buds showed the same 

 effect. With an eighth of C0 2 the average growth was 371 mg. and 



