148 VEGETABLE LIFE AND WORK. [SECTION 16. 



the product may be accumulated iu store for future growth, as iu the root 

 of the turnip, or the tuber of the potato, or the seed of com or pulse. 

 This store is mainly iu the form of starch. When growth begins anew, 

 this starch is turned into dextrine or into sugar, in liquid form, and used 

 to nourish and build up the germinating embryo or the new shoot, where 

 it is at length converted into cellulose and used to build up plant-structure. 



454. But that which builds plant-fabric is not the cellular structure 

 itself; the work is done by the living protoplasm which dwells within the 

 walls. This also has to take and to assimilate its proper food, for its own 

 maintenance and growth. Protoplasm assimilates, along with the other 

 three elements, the nitrogen of the plant's food. This comes primarily from 

 the vast stock in the atmosphere, but mainly through the earth, where it is 

 accumulated through various processes in a fertile soil, — mainly, so far as 

 concerns crops, from the decomposition of former vegetables and animals. 

 This protoplasm, which is formed at the same time as the simpler cellulose, 

 is essentially the same as the flesh of animals, and the source of it. It is 

 the common basis of vegetable and of animal life. 



455. So plant-assimilation produces all the food and fabric of animals. 

 Starch, sugar, the oils (which are, as it were, these farinaceous matters 

 more deoxidated), chlorophyll, and the like, and even cellulose itself, form 

 the food of herbivorous animals and much of the food of man. When 

 digested they enter into the blood, undergo various transformations, and are 

 at length decomposed into carbonic acid and water, and exhaled from the 

 lungs in respiration, — in other words, are given back to the air by the ani- 

 mal as the very same materials which the plant took from the air as its food, 

 — are given back to the air in the same form that they would have taken if 

 the vegetable matter had been left to decay where it grew, or if it had been 

 set on fire and burned ; and with the same result, too, as to the heat, — the 

 heat in this case producing and maintaining the proper temperature of the 

 animal. 



456. The protoplasm and other products containing nitrogen (gluten, 

 legumine, etc.), and which are most accumulated in grains and seeds (for 

 the nourishment of their embryos when they germinate), compose the most 

 nutritious vegetable food consumed by animals; they form their proper 

 flesh and sinews, while the earthy constituents of the plant form the earthy 

 matter of the bones, etc. At length decomposed, in the secretions and 

 excretions, these nitrogenous constituents are through successive changes 

 finally resolved into mineral matter, into carbonic acid, water, and ammonia 

 or some nitrates, — into exactly or essentially the same materials which the 

 plants took up and assimilated. Animals depend upon vegetables abso- 

 lutely and directly for their subsistence ; also indirectly, because 



457. Plants purify the air for animals. In the very process by which they 

 create food they take from the air carbonic acid gas, injurious to animal res- 

 piration, which is continually poured into it by the breathing of all animals, 

 by all decay, by the burning of fuel and all other ordinary combustion; and 



