May 23, 1913] 



SCIENCE 



793 



cumlocution. Bergen and Davis' have a sen- 

 tence which shows clearly how the restricted 

 usage conflicts with the general usage illus- 

 trated by the definition given above: 



The series of processes by which the plant 

 (1) takes in raw material to form its foods, (2) 

 unites these into foods, and finally (3) constructs 

 tissue from these foods or (4) stores them, consti- 

 tutes nutrition. 



Gager in a recent book-review^ has given 

 another excellent illustration of the same con- 

 flict of usages in the sentence which follows : 



On page 38, mineral nutrients are erroneously 

 called plant food. [The italics of both quotations 

 are mine.] 



Judging from these quotations, it is evident 

 that the content of the newer usage is entirely 

 different from the older general usage. Car- 

 bon dioxide, water and mineral salts, all 

 clearly to be classed as plant food under the 

 older definitions, can not be so classed accord- 

 ing to the newer usage. By a process of ex- 

 clusion, after a consideration of the quota- 

 tions just given, we arrive at the following 

 new definition of the word food, viz., organic 

 materials availahle for immediate assimila- 

 tion. It appears, however, from other discus- 

 sions that the intentions of the proponents is 

 to apply the term food also to the organic raw 

 material used by animals or colorless plants. 



Two questions arise from the foregoing con- 

 sideration: (1) Why has the new meaning of 

 "food" arisen? (2) Does it deserve to pre- 

 vail? 



The arguments for the restricted usage are 

 derived mainly from a comparison of the 

 nutrition of green plants with that of animals. 

 The food of an animal is chemically practi- 

 cally the same material as the tissues of the 

 animal and consists of proteins, oils, fats and 

 carbohydrates. (Mineral matter may be ex- 

 cluded from the consideration for the pres- 

 ent.) During the process of digestion, this 

 food is temporarily simplified as far as may 

 be necessary io make it soluble. Assimilation 



» " Principl^ of Botany," p. 106, 1906. 

 'Payne's "Manual of Experimental Botany," 

 Torreya, 12: 134. 



consists merely in the reconstruction of com- 

 pounds in general like those found in the 

 original food. In the case of green plants, all 

 the materials obtained from the surroundings 

 are simple inorganic substances. The process 

 of preparing them for assimilation is a com- 

 plex synthesis, carried on by means of energy 

 derived from an external source. At the end 

 of this process we find ready for assimilation 

 substances of the same sort as those which 

 result from animal digestion. The ensuing 

 process of assimilation is the same in green 

 plants as in animals. These differences and 

 similarities in materials and processes form 

 the basis for the revised definition of the word 

 food. 



The reasons for adopting the new definition 

 have been discussed in detail by Barnes." 

 They may be briefly recapitulated as follows : 

 Protoplasm, being the same in green plants as 

 in animals and colorless plants, and the ma- 

 terial which it can actually assimilate being 

 always organic, it creates an undesirable an- 

 tithesis in thought to recognize as food for 

 living things both inorganic and organic sub- 

 stances. Carbon dioxide and water if recog- 

 nized as food for green jalants can be so con- 

 sidered only for the chlorophyl-bearing cells, 

 and for these only in the presence of light. 

 They can not be used as food by the chloro- 

 phyl-less cells at any time, or for green cells 

 in the absence of light. 



Notwithstanding the weight and authority 

 of the arguments in favor of restricting the 

 meaning of the word food, there are numerous 

 objections which should be given considera- 

 tion. 



One of the principal objections to be noted 

 arises from the fact that the difficulty noted 

 by Barnes and others is mainly of academic 

 interest. So far as I have been able to dis- 

 cover, the question has been discussed only 

 in two treatises of plant physiology designed 

 for use by university students (Barnes and 

 Green). Apparently, then, to be thoroughly 

 conversant with the new usage, it is necessary 



= Coulter, Barnes and Cowles, ' ' Physiology, ' ' 

 3: 356-8. 



