NUTRITION 



357 



Is " food " food only for certain cells? — The first thing that awakens 

 suspicion as to the wisdom of this answer is that the living matter of green 

 plants is like that of all other living things, and it would be very strange 

 if in them protoplasm could be nourished with inorganic substances, 

 when in all others it requires organic material. Yet the green plant 

 might be differently constituted; and it is said by way of explanation that 

 this peculiarity is due to the presence of the green pigment, chlorophyll. 

 On examining this point, it is found that only a part of the plant has 

 chlorophyll. Most roots entirely lack it; only the outer cells of the stem 

 ever contain it; and there are many cells, even in a thin leaf, and a great 

 mass of them in a fleshy leaf, which are not green. Then we are forced 

 to state the matter thus: the green parts of green plants use inorganic 

 " food"; the colorless parts require organic food, for it is conceded on 

 all hands that the colorless cells are unable to utilize any carbon dioxid 

 and water. Whence it would seem that one cell might nourish itself with 

 inorganic " food " and its next neighbor be unable to do so. That would 

 certainly be a confusing situation if it could not be better described. 



Is " food " food only at certain times ? ^ It appears, further, that 

 carbon dioxid and water can be " foods " only part of the time ; namely, 

 when the green cells are adequately lighted. So except in the day, even 

 the green cell would require organic food! The situation would have 

 to be stated thus : The " food " of the green cells only, and only by day, 

 consists of carbon dioxid and water; the rest of the plant all the time 

 and the whole of the plant at night must have organic food like all other 

 living things. 



Antithesis avoidable. — A little consideration shows that the apparent 

 antithesis between green plants and other creatures is of our own making; 

 it is produced solely by the application of the term food to the sub- 

 stances which enter the body, irrespective of their role. This antithesis 

 can be avoided, and the confusion and contradiction eliminated, merely 

 by avoiding this inept use of the term food and by applying it to organic 

 substances only. By this expedient we escape a different use of the same 

 terms in plant and animal physiology, with its resultant confusion of 

 ideas, and we bring the green plants into line with all other beings, so 

 far as nutrition is concerned. Excluding the inorganic substances from 

 the category of foods, we need to recognize that one power possessed by 

 green plants is unique : they alone make their own food, and not their 

 own only, but food for the whole world. What they use for this food 

 making — carbon dioxid and water — may be distinguished as food ma- 



