438 Transactions. — Botany. 



part of the carbo-hydrates supplied to the cells. It is this 

 indirect oxidation that produces the carbon-dioxide that is 

 continuously given oif by living plants. This constructive 

 metabolic work of the protoplasm is an act that we cannot 

 explain in detail ; when we can, we shall indeed have solved 

 the mystery of life. We can only dimly perceive that the syn- 

 thesis depends on some peculiar power possessed by the pro- 

 toplasm of presenting the atoms and molecules to each other. 

 We may therefore suppose that the cell machinery of the 

 roots or the nodules is so exalted in activity by the presence 

 or the products of the bacteroids as to be able to force the 

 notoriously inert nitrogen into combination with other mole- 

 cules, so as to produce nitrates, or amides, or other similar 

 bodies. The energy required for this transformation is no 

 doubt supplied by the oxidation of part of the abundant stream 

 of starch and other carbo-hydrates, as well as salts, that is 

 conveyed to the nodules from the roots, the surplus of these 

 substances being alone available for entering into combination 

 with the nitrogen directly assimilated from the air. It has 

 been suggested that, as the sap expressed from the active 

 tissues of the nodules is alkaline, the cell protoplasm in the 

 presence of an alkali and free nitrogen may be able to build 

 up ammonium-nitrite or some such body. On this view, all 

 that seems required for the forcing of nitrogen into the organic 

 synthesis is a sufficient supply of carbo-hydrates. But this 

 does not explain the whole difficulty, else why cannot the 

 well-nourished cells of any plant do the trick ? 



Though we are unable, and are likely to remain unable, to 

 explain in detail the process of nitrogen fixation, the results of 

 the researches I have detailed do not on that account lose any- 

 thing of their importance. They constitute a clear and a most 

 valuable addition to our assured knowledge of the nutrition 

 of a large class of agricultural plants. To the farmer, the 

 forester, and the gardener, the new knowledge is of the very 

 highest significance. The farmer now knows that he has at 

 his disposal a simple, certain, and most economical means of 

 enriching his land in nitrogenous compounds by the spon- 

 taneous bounty of nature. To avail himself of this he needs 

 only to grow a judicious mixture of leguminous and grami- 

 neous plants in the same crop, or to use a suitable rotation of 

 leguminous and other crops in successive years. Clover, 

 lucerne, peas, beans, and sainfoin are good examples of useful 

 leguminous crops, and they all possess a very extensive and 

 well developed system of roots. When the crops are harvested 

 or eaten off by stock, the abundant root-system decays in 

 the soil, and leaves it much richer in nitrogenous compounds 

 than it was before. The soil is thus, by the mere act of na- 

 ture, endowed with large supplies of a prime necessary of 



