RESPIRATION AND OXYGEN. 83 



31 to 64 days, beans showed not only a quantitative decrease in the 

 wet and dry weight of shoots and roots, amounting in the case of the 

 latter sometimes to nearly one-third, but they were also shorter and 

 more bushy, with fewer rootlets. The roots of lupines and rye in a 

 mixture of 5 per cent CO2 were both more shallow and less developed, 

 while the roots of wheat were practically indifferent to the gas. 



Jaccard (1893 : 289) found that rarefied air brought about an 

 acceleration of growth, accompanied by modifications in the general 

 aspect of the plant, while air compressed between 3 and 4 atmos- 

 pheres frequently produced an acceleration of growth which was 

 weaker and less general than in the case of rarefied air. Its injurious 

 effect did not occur until a pressure of 8 atmospheres was reached. 

 When oxygen was added up to 90 per cent, there was in general no 

 injurious effect upon growth, and if such air was rarefied it brought 

 about an increased rate of growth. When a mixture containing 70 

 per cent of oxygen was compressed until the oxygen tension equaled 

 that of 10 atmospheres of air, growth was greatly hindered. 



Chudiakow (1894 : 333) investigated the effect of temperature 

 upon the length of Hfe in the absence of oxygen, using young seed- 

 lings of Vicia faba, Triticum vulgare, Pisum sativum, and Helianthus 

 annuus. The results showed that the increased respiration due to 

 higher temperature did not make the plants more resistant to the 

 consequences of the withdrawal of oxygen. On the contrary, in 

 spite of the greater rate of respiration or even on account of it, the 

 plants died much more rapidly than at low temperatures. Experi- 

 ments with swollen seeds of Brassica napus, Triticum vulgare, Vicia 

 faba, and Zea mays gave the same results. 



Recent researches. — In the case of roots of Vicia saliva and Pisum 

 sativum, Chapin (1902 : 375) observed that the slo wing-down of 

 growth was noticeable at 5 per cent CO 2 and growth stopped com- 

 pletely at 25 to 30 per cent. An injurious after-effect was not no- 

 ticed when 20 per cent CO2 acted for 120 hours. At 40 per cent no 

 significant damage was noticed after 24 to 28 hours, but if the plants 

 remained 72 to 96 hours in 20 to 40 per cent CO2, the after-effect 

 became evident. The formation of lateral roots was completely 

 suppressed in 20 to 25 per cent CO2. Seedlings of Pisum sativum 

 were unable to develop at 20 per cent and were killed at 25 per cent 

 in 96 hours. The corresponding values for Vicia saliva were 35 per 

 cent and 80 per cent in 40 hours. The hypocotyl of Sinapis and 

 Trifolium began to stop growth at 15 per cent and completely ceased 

 to grow at 25 per cent. The time necessary to kill plants in CO2 

 decreased as the content increased. With roots and shoots a small 

 amount of growth was still evident after 24 hours with all the higher 

 percentages of CO2, and the effect of the gas therefore was not 

 instantaneous. There was a great difference in the resistance to 



