RESPIRATION AND OXYGEN. 71 



wilted on the second day and badly on the third. It was then given 

 access to the air, but failed to recover. 



Summary. The depressing action of high percentages of carbon 

 dioxid upon absorption and transpiration has been shown in all the 

 investigations concerned. A similar result has been obtained by 

 Livingston and Free by the use of nitrogen. In practically all cases 

 the pure gas was employed, and hence it is uncertain at what points 

 injury begins. It appears probable that with many species a dis- 

 turbance of the water-relations occurs at 5 or 10 per cent, or even 

 lower, and that in water-logged soils and in bogs carbon dioxid may 

 operate by reducing absorption as well as respiration and photo- 

 synthesis. Kossowitsch was the first to show that C0 2 exerted a 

 specific effect, regardless of the presence of oxygen, and this was 

 confirmed by Kosaroff, who emphasized the fact that the injury 

 wrought was due to the poisonous property of carbon dioxid as well 

 as to the withdrawal of oxygen. The results of Burgerstein with 

 exceedingly dilute solutions do not contravene the rule, but serve 

 to show that carbonic acid in minute quantities behaves like many 

 other acids that stimulate absorption and transpiration. 



GERMINATION. 



Early researches. The earliest studies of germination in a vacuum 

 were made by Boyle (1660), Ray (1686), Homberg (1699), Boer- 

 haave (1724), and Musschenbroek (1729). Their results were all in 

 agreement to the effect that seeds germinated poorly or not at all in 

 vacua, though they did readily upon renewed access of air. Hum- 

 boldt (1794) and Rollo (1798) concluded that seeds germinated more 

 readily in oxygen than in ordinary air, while Huber and Senebier 

 (1801) found that germination was poorer in oxygen obtained chemi- 

 cally. Rollo also determined that seeds would not grow in hydrogen 

 or nitrogen. Ingenhousz (1786) germinated cress seeds in oxygen, 

 but was unable to do so in hydrogen. 



Lefebure (1801 : 94) investigated the germination of radish seeds 

 in a number of gases. When placed in nitrogen, they failed to ger- 

 minate during a sojourn of 12 days, while in oxygen nearly all had 

 germinated by the end of 3 days. Repeated experiments gave the 

 same results in oxygen. No germination occurred in carbon dioxid 

 or in hydrogen in a period of 12 days. When oxygen was mixed with 

 nitrogen, carbon dioxid, hydrogen, or a combination of nitrogen and 

 C0 2 in the proportion of 1 to 8 or 1 to 16 parts, the seeds germinated 

 as readily as in ordinary air. When the amount of oxygen was re- 

 duced to one thirty-second, however, some failed to grow and the 

 others did so more slowly than in the air. 



Huber and Senebier (1801) were the pioneers in an exhaustive 

 study of the relation of air and other gases to germination. Inter- 



