THEORETICAL CONSIDERATIONS 267 



the role of the phytohaematin, but also the relation of aerobic res- 

 piration, anaerobic respiration, and alcoholic fermentation, and the 

 essential identity of the respiratory process in plants and animals. 

 Doubtless further researches will make necessar}- certain modifica- 

 tions of this diagram, but it serves to present concisely our present 

 knowledge of respiration, and to emphasize the complexity of the 

 process. 



For our purpose three points in these conceptions are to be em- 

 phasized : first, that the act of respiration is complex ; second, that 

 some of the steps apparently do not involve living matter at all, but 

 are purely non-vital, chemical changes ; third, that the processes not 

 onl}' of normal, aerobic respiration, but of anaerobic respiration and 

 fermentation as well, involve the action of enzymes. Thus it is 

 clearly evident that radium rays, or any other stimulus, may affect 

 respiration in a variety of ways by modifying any of the steps in- 

 volved. Not only may the living protoplasm (or some intermediate 

 biogen molecule) be stimulated, but the action of the various enzymes 

 may be accelerated or retarded or completely inhibited, or the phy- 

 tohaematin may be similarly affected or completely destroyed. 

 Also, under certain conditions, the protoplasm may be stimulated to 

 produce these substances in greater or less quantity, or not at all. 



Germination: The mystery of the so-called "resting" seed is 

 yet to be solved. We understand a few things, however, about its 

 physiology. We know it is not dead, for it is constantly, at least at 

 ordinary temperatures, slowly undergoing certain changes which 

 characterize metabolism everywhere. These changes in time are 

 sufficient to destroy the power to resume the normal rate of the life 

 processes which, with the ripening of the seed, became reduced to 

 their lowest terms. 



The resting seed consists, in addition to its integuments, of at 

 least three essential things: (i) The embryo; (2) the nourishment 

 stored in or around the embryo ; (3) enzymes, secreted largely if not 

 wholly by the embr3'o.* Investigations were made byAlbo^-^for 

 the purpose of finding out why seeds, apparently normal so far as 

 structure and chemical composition are concerned, lose their vitality, 

 even though the stored food remains in abundance. He found that 



* Pond's*- studies on the capacity of the date endosperm for self-digestion indicate 

 that the enzymes active in the germination of seeds originate, not as was formerly be- 

 lieved, within the endosperm, but wholly within the embryo. I have reviewed the 

 literature on this subject elsewhere. ^^ 



