142 PLANT PHYSIOLOGY 



in animals by breathing, or forcible muscular passage thereof in and out of 

 the body. 



It has of late been insisted by some of the younger physiologists of America 

 that the processes of photosynthesis and respiration- are not comparable 

 reciprocally point by point as often taught by our current books. In some 

 part the objection is well taken, but in much larger part it is simply a phase 

 of the tendency to over-refinement of thought and expression apt to accom- 

 pany too concentrated a specialization. Since all organic substance of 

 both plants and animals starts from basal carbohydrate, which is formed 

 with storage of energy from carbon dioxide and water, and since in the long 

 run all organic substance, whether by respiration or decay, returns to carbon 

 dioxide and water with release of the equivalent energy, it is quite plain 

 that in the long run, that is, in the sums total, the two processes are strictly 

 comparable. Moreover this is true even within much narrower limits, 

 and it is even possible, as the instructive case of fermentation shows, that 

 respiration in plants is a decomposition of carbohydrates saturating the 

 protoplasm rather than of the protoplasm itself, the regular exchange of 

 the gases being complicated by accessory chemical reactions, in part inci- 

 dental and in part ecological. At all events, if safe-guarded by the knowl- 

 edge that, of the photosynthate formed, only a part is soon used up in respira- 

 tion (though in the end it all is), and that the steps in respiration are rrany 

 and complicated while in photosynthesis they are few and direct, then the 

 two processes are, even though somewhat conventionally, comparable. 



Literature of Respiration. In addition to the general works 

 of Pfeffer, Jost, and Verworn, there is much on this subject in 

 the papers by Sachs, by Brown, and by Blackman, cited earlier 

 under Literature of Photosynthesis. There is also a very valuable 

 address by Barnes, "The Theory of Respiration," in the Botanical 

 Gazette, 39, 1905, 81 (and in Science, 21, 1905, 241). On fermenta- 

 tion the basal work is Green's "The Soluble Ferments and Fermen- 

 tation," Cambridge, 1901, while the most useful works upon yeast 

 fermentation are Matthews' "Manual of Alcoholic Fermentation," 

 London, 1902, and a very valuable lecture by van't Hoff in his 

 "Physical Chemistry in the Service of the Sciences," Chicago, 1904. 

 On the nature of the release of energy in the organism (animal, but 

 applicable in principle to plants), there is a good article by Thurston 

 in Science, 1, 1895; 365. 



6. ABSORPTION. 



In the foregoing study of the formation, transformation, 

 and deformation of the organic substances of the plant, we have 

 more than once been brought into touch with problems involv- 

 ing the mode of movement of the substances. Obviously these 

 are problems of physics, primarily concerned with the energy 



