RESPIRATION OF PLANTS 89 



the lower plants, the fungi and bacteria. Their activity explains 

 the phosphorescence of rotted wood, sea fish, meat, etc. Phos- 

 phorescence may be due simply to oxidation by the air of special 

 phosphorescing bodies of protein character produced by the 

 organism. 



According to the data of Gurvitch, root ends and some other 

 parts of the plant where there is an intense multiplication of 

 cells emit '^ mitogenetic rays," which are capable of stimulating 

 the process of division in dormant cells. These rays are of a 

 very short wave length (about 2500 A.) and lie beyond the limits 

 of the visible spectrum in the region of the ultraviolet rays. No 

 definite proof, however, has been supplied of the existence of 

 mitogenetic rays. 



21. Substances Consumed during Respiration. The Respira- 

 tory Quotient. — The fundamental respiratory materials, as has 

 been seen, are the sugars, especially fructose. From the general 

 equation of respiration, 



CeHiaOe + 6O2 -> 6CO2 + 6H2O, 



it is clear that the volume of the gases exchanged, viz., the 

 oxygen absorbed and the carbon dioxide liberated, must be equal. 

 A plant placed in a closed container, therefore, does not alter 

 the volume of air, though it changes its composition, substituting 

 carbon dioxide for oxygen. In the more typical cases, the ratio 

 of carbon dioxide to oxygen in respiration, C02:02, called the 

 ''respiratory quotient," is equal to unity. 



There are many deviations from this general rule, as very 

 often the respiratory quotient is less than unity. Sometimes, it 

 is more. Various causes may be responsible for these differences. 

 Besides the end products of oxidation, CO2 and H2O, frequently 

 there are formed but partly oxidized compounds — such as oxalic 

 acid, C2O4H2; tartaric acid, C4O6H6; etc.— which contain more 

 oxygen than carbohydrates do. When these substances are 

 produced, part of the absorbed oxygen remains in the plant, and 

 the ratio of CO2: O2 is less than unity. On the other hand, when 

 oxygen is deficient, as in the respiration of bulky organs or seeds 

 immersed in water, normal respiration may be accompanied 

 by alcoholic fermentation, resulting in the liberation of carbon 

 dioxide without absorption of oxygen from the air. In such 

 cases, the respiratory quotient will be greater than unity. 



