330 ASSIMILATION. 



lished the results of a series of experiments upon the subject of 

 the appropriation of nitrogen by plants. These experiments were 

 designed to settle the disputed question. Ever}" conceivable pre- 

 caution was taken to avoid any error, and the plants were grown 

 under conditions as little unlike their ordinary surroundings as 

 possible. Under these conditions to insure healthy growth, they 

 were deprived of all access to nitrogen except as it existed in 

 the free state in the atmosphere or dissolved in the water sup- 

 plied to them. It was found that no plants appeared to make 

 use of the free nitrogen of the atmosphere or of the nitrogen 

 dissolved in water supplied to their roots. But in certain cases, 

 especially of leguminous plants cultivated in the open air, there 

 is an apparent gain in the amount of nitrogenous products in 

 the plant over and above that which is directly attributable to 

 the combined nitrogen furnished to it. 1 



1 The following extracts from the paper by Lawes, Gilbert, and Pugh will 

 convey a clear idea of the cautious manner in which their important results 

 are reported : 



" The results obtained with Graminacese in 1858 . . . point without excep- 

 tion to the fact that under the circumstances of growth to which the plants were 

 subjected, no assimilation of free nitrogen has taken place. The regular pro- 

 cess of cell-formation has gone on ; carbonic acid has been decomposed, and 

 carbon and the elements of water have been transformed into cellulose ; the 

 plants have drawn the nitrogenous compounds from the older cells to perform 

 the mysterious office of the formation of new cells ; those parts have been de- 

 veloped which required the smallest amount of nitrogen, and all the stages of 

 growth have been passed through to the formation of glumes, pales, and awns 

 for the seed. In fact, the plants have performed all the functions that it is 

 possible for a plant to perform when deprived of a sufficient supply of com- 

 bined nitrogen. They have gone on thus increasing their organic constituents 

 with one constant amount of combined nitrogen until the percentage of that 

 element in the vegetable matter is far below the ordinary amount of it, that 

 is, until the composition indicates that further development had ceased for 

 want of a supply of available nitrogen. Throughout all these phases, water 

 saturated with free nitrogen has been passing through the plant ; nitrogen dis- 

 solved in the fluid of the cells has constantly been in the most intimate contact 

 with the contents of the cells and with the cell-walls " (p. 523). 



Of leguminous plants the investigators say, " In those cases in which we 

 have succeeded in getting leguminous plants to grow pretty healthily for a 

 considerable length of time, the results, so far as they go, confirm those ob- 

 tained with Graminaceae, not showing in their case, any more than with the 

 latter, an assimilation of free nitrogen " (p. 526). 



Further, they say, " From the results of various investigations, as well as 

 from other considerations, we think it may be concluded that under the cir- 

 cumstances of our experiments, on the question of the assimilation of free 

 nitrogen by plants, there would not be any supply to them of an unaccounted 

 quantity of combined nitrogen due either to the formation of oxygen com- 



