202 THE FOOD AND NUTRITION OF PLANTS. 



and all parts of recent formation, such as the buds, young shoots, 

 and rootlets, always contain several hundredths of it. This gives 

 the reason, also, why sap-wood is so liable to decay (induced by 

 the proteine), and the more liable in proportion to its newness and 

 the quantity of sap it contains, while the perfectly lignified heart- 

 wood is so durable. Following this course, we find that the az- 

 otized matter rapidly diminishes in the stem and herbage during 

 flowering, while it accumulates in the forming fruit, and is finally 

 condensed in the seeds (which have a larger percentage than 

 any other organ), ready to subserve the same office in the devel- 

 opment of the embryo plant it contains.* 



357. When wheat-flour, kneaded into dough, is subjected to the 

 prolonged action of water, the starch is washed away, and a tena- 

 cious, elastic residue, the Gluten of the flour, which gives it the 

 capability of being raised, contains nearly all the proteine com- 

 pounds of the seed, mixed with some fatty matters (which may be 

 removed by alcohol and ether) and with a little cellulose. The 

 azotized products constitute from eight to thirty per cent, of the 

 weight of wheat-flour ; the proportion varying greatly under differ- 

 ent circumstances, but always largest when the soil is best supplied 

 with manures that abound in nitrogen. The gluten is not itself a 

 simple quaternary principle ; but is a mixture of four nearly isom- 

 eric bodies of this sort, distinguished by chemists under the names 

 Fibrine (identical in nature with that which forms the muscles of 

 animals), Albumen (of the same nature as animal albumen), Ca- 

 seine (identical with the curd of milk), and Glutine. In beans and 

 all kinds of pulse, or seeds of Leguminous plants, the large pro- 

 portion of azotized matter principally occurs in the form of Legu- 

 mine, a form nearly intermediate in character between albumen 

 and caseine. 



358. Having now noticed all the principal products of assimila- 

 tion in plants, at least those concerned in nutrition, as compared 

 wjth the inorganic materials from which they must needs be 

 formed, we may the more clearly perceive, that the principal re- 

 sult of vegetation, as concerns the atmosphere, from which plants 

 draw their food, consists in the withdrawal of water, of a little am- 



* The cotyledons of peas and beans, according to Mr. Rigg, contain from 

 100 to 140 parts, and the plumule abcut 200 parts, of nitrogen to 1,000 parts of 

 carbon. 



