EESPIRATION AND OXYGEN. 



15 



during the day a greater amount of CO 2 than at night. This 

 difference between the day and night volumes of CO2 was more 

 important when the plants were most fleshy. Plants exhibited a more 

 active gas-exchange in proportion as their fleshiness is less 

 pronounced, and hence ordinary plants showed a greater respiration 

 intensity than fleshy ones. Among fleshy plants, Crassulacece and 

 Mesembryanthemacece, which possess a thin cuticle, exhibited a more 

 active exchange than most of the Cactacece. The fleshy euphorbias 

 and trees with evergreen leaves were nearly intermediate in this re- 

 spect. The extent of surface-contact with the atmospheric air was 

 regarded as of the first importance in explaining differences in in- 

 tensity and respiration, and the amount of water the plant contains 

 as next most important. 



Aeroboe (1893) studied the respiration of roots of Vicia faba in 

 relation to light and reached the conclusion that this exerted an 

 indirect effect. He found that when plant parts were placed in the 

 dark the production of CO 2 steadily decreased. 



Bohm (1893), in a study of the respiration of potatoes, found that 

 wounding, relatively low and high temperatures, partial exclusion 

 of oxygen, continued exposure to pure oxygen, and infection by 

 Phytophthora infestans, all produced energetic respiration. In a 

 medium poor in oxygen, thin cyhnders of sound or stimulated tubers 

 used only a small amount of the gas. 



Mangin (1896 : 747) in experiments with flax, radish, peas, car- 

 rots, etc., found that the accumulation of CO2 and a reduction in 

 oxygen effects a diminution of respiratory activity in the seeds and 

 tubers. This occurred in air that contained 1 to 3 per cent of CO2 

 in one case and 2 to 5 per cent in the other. 



Jost (1893 : 100) observed that wounded potatoes, especially those 

 cut into many pieces, showed earlier growth of the buds. Ziegenbein 

 (1893 : 594) determined the respiration rate of potato tubers, seed- 

 lings, and shoots at different temperatures to be as follows, expressed 

 in miUigrams of CO2 produced by 100 gm. in an hour. 



Czapek (1896 : 321) studied the 

 excretions of roots of Phaseolus, 

 Pisum, Helianthus, Cucurbita, Zea, 

 Linum, Picea, etc., in water and in 

 air saturated with moisture. He 

 found that the roots of all of these 

 secrete various substances, partly 

 organic, partly inorganic. The lat- 

 ter are potassium, calcium, mag- 

 nesium, and hydrochloric, sulphuric, 

 and phosphoric acids. Of these, 

 only potassium and phosphoric acid 

 are present in any considerable 



Table 2. 



