RESPIRATION 27 



stress of circumstances ; third, physiological rearrangement 

 of atoms into simpler molecules, also really intramolecular 

 respiration, the anaerobic normal respiration of a compara- 

 tively small number of invariably low organisms. 



INTRAMOLECULAR RESPIRATION 



Having examined the first of these allied processes as 

 thoroughly as our limits allow, let us pass to the second. 

 From experiments hitherto conducted, it would seem that 

 the germinating seeds of higher plants are better able to 

 survive without a copious supply of oxygen than are the 

 other parts. This is what might be expected, for the em- 

 bryo in the seed, when it becomes active in germination, is 

 a very vigorous organism, usually well supplied with just 

 such foods as may be readily broken down into simpler 

 compounds. The seeds of pea, for example, stimulated to 

 germinate by being soaked in water at room-temperature 

 for twelve or fifteen hours, will continue to respire actively 

 for forty-eight hours or longer, even in a vacuum, producing 

 carbon-dioxide in nearly the same quantity as under the 

 same conditions of temperature, etc., in ordinary air. Of 

 course some air containing free oxygen will be carried into 

 the vacuum by the peas, but this will very soon be entirely 

 consumed in normal respiration, and the continued supply 

 of energy must be obtained by intramolecular respiration. * 

 Comparative investigations have shown that different 

 plants and different organs vary considerably in their abil- 

 ity under stress to substitute intramolecular for normal 

 respiration, and that in very few of the higher plants is 

 intramolecular respiration, as measured by the yield in 

 carbon-dioxide, so effective as normal respiration. 



.Exir all of the higher plants prolonged intramolecular 

 respiration is jmpossible. To what this is due is not wholly 



* For directions for laboratory and demonstration experiments on this 

 subject consult Darwin & Acton's Practical Physiology of Plants ; Moor's 

 translation, under similar title, of Detmer's Pflanzenphysiologisches Prak- 

 tikum, or the special papers on the subject cited in Pfeffer's Handbuch der 

 Pflanzenphysiologie, and its English translation, and also in Ganong's and 

 MacDougal's manuals. 



