28 PLANT PHYSIOLOGY 



clear. The substances first broken up in intramolecular 

 respiration are the same as in normal respiration, namely, 

 the sugars, starches ( after conversion into sugars ) , and the 

 fats and oils; but later the proteid substances enclosed in 

 the cell, and finally the living substance itself, are decom- 

 posed to supply needed energy. Whether the cessation of 

 intramolecular respiration in experiments upon higher 

 plants, and the consequent death of the organism, are due 

 to the destruction of a part of the living substance, or 

 whether they are due to the production in the cells of 

 poisonous substances, cannot now be positively asserted. 

 Certain it is that for higher organisms intramolecular 

 respiration is a function very limited in importance, taking 

 place only under the stress of continued need of energj-, in 

 the absence of an adequate supply of free oxygen, and 

 capable of being maintained for comparatively brief periods 

 only. Like normal respiration, it is carried on solely by the 

 living protoplasm, more or less actively according to the 

 greater or lesser activity of the protoplasm ; the substances 

 decomposed are like those oxidized in normal respiration 

 and differ in different species of plants; the products differ 

 according to the plant, the conditions under which it acts, 

 and the substances acted upon. 



Besides carbon-dioxide, alcohol may be produced in con- 

 siderable amount — suggesting the connection between fer- 

 mentation and intramolecular respiration — and also organic 

 acids, together with small amounts of many other com- 

 pounds. In germinating peas, the alcohol produced may 

 equal as much as h% the weight of the moist seeds,* enough 

 to give some support to the hypothesis suggested above 

 that it may be the accumulation of the poisonous pro- 

 ducts of intramolecular respiration which, as we shall see is 

 the case in fermentation (pp. 30-37), brings about the 

 cessation of respiration and the death of the organism. 



Between those plants for which aerobic respiration is in- 

 dispensable to normally active life, and for which anaerobic 

 respiration is only a means of maintaining life over un- 



* Godlewski. In the Anzeiger der-Krakauer Akademie, Juli, 1897. Re- 

 viewed in Botaniache Zeitung, Sept. 16, 1897. 



