No. 414.] NORMAL RESPIRATION. 473 
have recourse under stress of circumstances ; third, physiologi- 
cal rearrangement of atoms into simpler molecules, also intra- 
molecular respiration, but the anaérobic normal respiration of 
a comparatively small number of invariably low organisms. 
From experiments hitherto conducted, it would seem that 
the germinating seeds are better able to survive without a 
copious supply of oxygen than are the other parts of higher 
plants. This is what, a priori, might be expected, for the 
embryo 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 for twelve to fifteen hours in water at room tempera- 
ture, will continue to respire actively for forty-eight hours or 
more, 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 exhausted in normal respiration. ^ The con-, 
tinued supply of energy must be obtained by intramolecular 
respiration. Comparative investigations show that different 
plants and different organs vary considerably in their ability 
to substitute under stress 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. 
For all higher plants prolonged intramolecular respiration 
is impossible. To what this is due is not wholly clear. The 
substances first attacked in intramolecular respiration are the 
same as in normal respiration, Z.e., the sugars, starches (after 
conversion into sugar), and the fats and oils. Later the 
proteid substances enclosed in the cell, and finally the living 
Substance itself, are decomposed to supply needed energy. 
Whether the cessation of intramolecular respiration in experi- 
ments upon higher plants, and the consequent death of the 
Organism, are due to the destruction of part of the living 
substance, or to the production in the cells of poisonous sub- 
Stances, cannot now be determined. Certain it is that for 
