6 PLANT RESPIRATION 



From this table it is apparent that in some cases the energy 

 of plant respiration is not less than that of animal respiration. 

 The respiration of microorganisms is particularly intensive dur- 

 ing the period of a rapid development. The mold Aspergillus 

 niger is noted for its fabulous speed of growth. In 2 to 3 days 

 rank, matted layers of mold develop on suitable nutrient solu- 

 tions. The rate of respiration of Aspergillus niger is correspond- 

 ingly extraordinary among the lower organisms. 



In the case of seed-plants the rate of respiration is also 

 dependent to a marked degree upon the rate of growth.'' To 

 be sure, resting seeds show a decHne in weight which is traceable 

 in part to loss of water and in part to respiration, yet it is 

 evident from the direct quantitative determinations of Kolk- 

 witz,^ that the respiration of resting seeds is utterly unimpor- 

 tant. The respiratory energy of i kg. of seeds is i cc. of CO2 

 [for 24 hours] with a water content of 10-11%. It is worthy of 

 note that an increase of the water content of seeds to 33% 

 increases the C02-formation to 1200 cc. per kilogram. Of 

 course it remains undecided whether this process is to be 

 regarded as true respiration or merely as a spontaneous autoxi- 

 dation of various labile substances contained in the seed coats. ^ 

 Completely soaked seeds Hberate very considerable amounts 

 of COo. 



In the course of the germination of the seed the rate of growth 

 increases during the first days, then gradually becomes smaller. 

 The graphic representation of the process gives the so-called 

 grand curve of growth. If one follows the course of respiration 

 during the grand period of growth, one obtains the so-called 

 grand curve of respiration of germinating seeds. ^ It is similar 



jvl iKolkwitz, R. Ber. d. bot. Ges. 19: 285; 1901; see also Muntz. Compt. rend. 92: 97, 

 •j X3-. 1881. 



^ 2Becquerel, R. Compt. rend. 138: 1347- 1904; 143: 974. n"". 1906; Ann. sci. nat. 

 Bot. (IX) 5: 193. 1907. 



3 Mayer, A. Landwirtschaftl. Versuchs-Stationen 18: 245-270. 187s; Rischawi. Ibid. 

 19: 321-340. 1876. The first determination of respiration of germinating seeds we owe 

 to de Saussure. M6m. soc. phys. de Geneve 6: SS7. 1833. 



^ The respiration of plants older than seedlings has been followed by Kidd, 

 West and Briggs (Proc. Roy. Soc. London. B. 92:368. 1921) in the case of 

 Hdianthiis annuiis. Their respiratory index declines steadily with increasing 

 age of the plant. Hover and Gustafson (J. Gen. Physiol. 10: 33-39- 1926-27) 

 observed a decrease followed by a gradual increase after middle age, using leaves 

 of cereal plants. — Ed. 



