10 AERATION AND AIR-CONTENT. 



evergreens, both broad-leaved and needle-leaved, the range was from 

 0.8 to 4 times and the average 2 times the volume. For terrestrial 

 herbs, the range was from 0.5 for Liliuin to 5 for Triticum, and the 

 average 2.4 times the volume. Aquatic and marsh herbs varied 

 from 0.7 for Alisma plantago to 2.3 for Lythrum and Carex, the aver- 

 age being 1.6 times the volume, while the range in fleshy plants was 

 from 0.6 for Saxifraga cotyledon to 1.7 for Sedum and Mesembryan- 

 themum. The average was 1.1 times the volume. In most cases 

 the respiration was 50 to 100 per cent greater in May or June than 

 in September. 



To obtain further proof of the need for oxygen, Saussure treated 

 the roots of the chestnut with nitrogen, hydrogen, and carbonic 

 acid, using other plants in atmospheric air as checks. The plants 

 whose roots were in contact with CO2 died first at the end of 7 or 

 8 days, while those with the roots in nitrogen and hydrogen died at 

 the end of 13 or 14 days. The chestnuts with roots growing in 

 ordinary air were still vigorous at the end of 3 weeks, when the experi- 

 ment was finished. The conclusion that the presence of oxygen is 

 necessary for growth was further supported by the observation that 

 plants with roots submerged in stagnant water suffered more quickly 

 than those in running water, and also by the fact that roots which 

 grew^ into manure or into water conduits became very greatly divided 

 in the endeavor to increase their contact with the very small amount 

 of oxygen found in such places. 



Grischow (1819 : 143) determined that roots take up oxygen and 

 give off carbon dioxid. He likewise proved that fungi absorb oxy- 

 gen and evolve carbon dioxid, and hence that their respiration is 

 essentially the same as that of green plants. 



Marcet (1829) thought to have demonstrated that fungi also evolve 

 hydrogen in respiration, but later (1834) concluded that this was due 

 to fermentation processes set up by bacteria and that fungi respired 

 in the usual manner. 



Meyen (1838) declared that respiration is general for all plant 

 parts, and he also distinguished clearly between respiration and 

 photosynthesis in the economy of the plant. 



Dutrochet (1840) stated that, since all plant parts absorb oxygen 

 and excrete carbon dioxid, they should also produce heat, and he 

 was able to demonstrate this experimentally. He also emphasized 

 the need of distinguishing between respiration and the decomposition 

 of CO2 in the hght, and determined that neither periodic nor tropistic 

 movement was possible in the absence of oxygen. 



Becquerel (1833), Wiegmann and Polstorff (1842), and Oudemans 

 and Rauwenhoff (1858) early demonstrated that the excretion of the 

 root was acid, as shown by its reaction to litmus. 



Garreau (1851), in the study of respiration in the different organs 

 of various plants, determined the amount of CO2 exhaled by the 



