RESPIRATION AND OXYGEN. 73 



nitrogen. In the best vacuum obtainable some seeds, such as peas, 

 germinated to the point of the appearance of the radicle, but no 

 further. Seeds were unable to germinate in pure carbon dioxid, and 

 even a small amount retarded germination, both in sun and shade. 



John (1819 : 282) found that swollen peas showed no germination 

 after 4 weeks in carbon dioxid in the light, but that they began to 

 germinate in 3 days in a mixture of one-third carbon dioxid and two- 

 thirds ordinary air. No further growth occurred in the course of 

 2 weeks, even with access of air, as decomposition had set in. He 

 concluded that CO2 killed the embryo as well as the young seedling, 

 and that germination was possible only when the amount of air 

 exceeded that of carbon dioxid. 



Dobereiner (1822 : 212) germinated barley in one-half normal 

 atmospheric pressure and under a pressure of 2 atmospheres. The 

 germination proceeded at an equal rate under both bell-glasses, 

 but the seedlings grew faster in the compressed air than in the 

 rarefied. 



Later researches. — Bohm (1873) observed that wet seeds in pure 

 oxygen at the ordinary pressure did not go beyond the first stage 

 of germination, but that they thrived just as well as in atmospheric 

 air when the oxygen was mixed with four-fifths of its volume of 

 hydrogen or reduced to a pressure of 150 mm. The development of 

 beans was at a minimum in the case of seeds in pure oxygen. It was 

 not the lack of nitrogen but too high a pressure of oxygen that pro- 

 duced this, since the germination of the bean proceeded normally 

 in pure oxygen when the pressure was reduced to one-fifth of the 

 normal. The same amount of oxygen was absorbed when the ger- 

 mination took place in pure oxygen or in the air. He obtained the 

 same results with peas, lentils, and corn, while seeds of sunflower, 

 cress, and flax were much less influenced by high oxygen-pressure. 

 The development of the seedlings was somewhat weaker in pure 

 oxygen than in ordinary air. The results also indicated that oily 

 seeds can germinate under a much higher oxygen-pressure than 

 starchy ones. He later found (1874 : 180) that germination was 

 delayed by 5 per cent CO2, while in germinating cress the formation 

 of chlorophyll was delayed by 2 per cent CO 2, prevented by 20 per 

 cent, and entirely suppressed by 2 days' stay in the gas. 



Deh^rain and Landrin (1874 : 382) determined that seeds germi- 

 nate in pure oxygen, but less rapidly than in atmospheric air. When- 

 ever oxidation in the seed had begun, it continued even in an atmos- 

 phere deprived of oxygen, and the volume of CO 2 produced was 

 greater than the original volume of oxygen. Hydrogen appeared 

 ordinarily only in an atmosphere in which the oxygen had com- 

 pletely disappeared, and carbon dioxid was shown to be more 

 injurious to germination than nitrogen or hydrogen. 



