RESPIRATION AND OXYGEN. 9 



for 48 hours. The movement of the protoplasm ceased, but it 

 began again in 8 to 12 hours after the plants were returned to atmos- 

 pheric air. Scheele (1777) was the first to prove that oxygen was 

 used during germination and carbon dioxid released, as in animals. 

 Ingenhousz (1779) was the pioneer in recognizing that plants give 

 off carbon dioxid at night or in the dark, in contrast to the evolu- 

 tion of oxygen during the day. He stated that roots, flowers, and 

 fruits, as well as green parts, behaved in this manner. In 1796, he 

 emphasized the fact that roots and other colorless parts always 

 excrete C0 2 , while green parts in the light give off oxygen. He 

 likewise denied that plants absorb their necessary carbon from the 

 soil by means of the roots. 



Senebier (1791) stated that the access of ah- is indispensable to 

 plant life and that it was likewise necessary to the germination of 

 seeds in the soil. He also pointed out that the roots of plants perish 

 in stagnant water. Huber and Senebier (1801) found that the 

 amount of air during germination diminished in proportion to the 

 oxygen in it, and that this was accompanied by the formation of 

 carbon dioxid. They likewise noted that seeds would not germinate 

 in air whose oxygen had been exhausted by bees and they confirmed 

 the need of oxygen for plant-growth by a comprehensive series of 

 studies in various gases. Rollo (1798) believed that oxygen dis- 

 appeared and was replaced by carbon dioxid in the course of germi- 

 nation, and he determined that barley grains gave off CO 2 for several 

 days in the absence of oxygen. 



Saussure (1804) regarded water and oxygen as the two factors 

 essential to germination and stated that a small amount of oxygen 

 is present even in the case of the seeds of water-plants and others 

 that germinate under water. He proved this by showing that peas, 

 lentils, and seeds of Alisma and Polygonum were unable to germinate 

 in an amount of boiled water 7 to 8 times their weight, but did so 

 readily when the amount was 200 times greater. He further showed 

 that oxygen disappears and is replaced by carbon dioxid when the 

 seeds are in direct contact with it, but, when oxygen is scanty or 

 lacking, decomposition results, with the evolution of hydrogen as 

 well as carbon dioxid. The amount of oxygen necessary to effect 

 germination differed with the species, beans, kidney-beans, and lettuce 

 requiring more than peas, and these more than wheat, barley, or 

 purslane. 



Roots of carrot consumed their own volume of oxygen, as did 

 turnip, while a potato used 0.4 of its volume and a lily-bulb approxi- 

 mately the same. These differences were reflected in those of the 

 leaves. Leaves of deciduous trees and shrubs consumed from 2.2 

 to 8 times their volume of oxygen in 24 hours, beech and apricot 

 being the most active and lilac the least. The average consumption 

 for the 15 species was approximately 6 times the volume. For 



