GIVEN OFF BY PLANTS DURING THEIR GROWTH. 



59 



the differences are of course dependent on the same circumstances 

 as those already alluded to. 



It is a striking fact, that (excepting a single clover plant, which 

 was always unhealthy) there is in every case more than 200 grains 

 of water passed through the plant for one grain of material accu- 

 mulated — an amount which, when calculated to the average or at 

 least frequent produce of an acre of land, would very far exceed 

 the annual fall of rain. 



Referring to the column of water evaporated to mineral matter 

 fixed, we see the amount of the former to be, on an average, 2000 

 times that of the latter. Whatever other explanation, therefore, 

 we may receive as to the conditions of assumption of the plant 

 of some mineral substances occurring in it, in insoluble combi- 

 nations, we have here evidence sufficient to show that few of the 

 substances required by plants, and which are generally assumed 

 to be insoluble, are incapable of being taken up by them in an 

 adequate quantity in rain water. 



It was our hope to have given in this paper the results of the 

 determinations of nitrogen, in the various specimens grown in 

 the pots, with the view of showing what relation subsisted 

 between the amount of nitrogenous proximates fixed in the 

 plant, and that of the water passed through it. Unfortunately, 

 however, the laboratory work in connection with this branch of 

 the inquiry is as yet not so far advanced as to justify the dis- 

 cussion of the numerical results on this occasion, nor will our 

 allotted time allow us to do so. We may, however, state that 

 as far as our results have gone, it would appear that whilst for a 

 given quantity of water evaporated the amount of non-nitrogenous 

 substances fixed in the plant is within somewhat narrow limits 

 identical, in the specimens now under experiment of the two 

 natural orders of plants, that of the nitrogenous proximates fixed 

 is, on the other hand, about twice as great in the Leguminosse as 

 in the Graminaceae. This is indeed a significant fact, as bearing 

 upon the distinctive functional characters of the various plants 

 which enter into rotation. It is, moreover, perfectly consistent 

 with the results of our experiments in the field with wheat and 

 beans respectively, which show that under the same circumstances 

 of growth, as to manure, &c, and in the same season, the acreage 

 yield of nitrogen is twice or thrice as great in beans as in wheat. 



It cannot be supposed, however, that with the larger amount 

 of nitrogen harvested in the leguminous crop the soil would be 

 proportionally exhausted of it, for common practice sufficiently 

 teaches that, other things being equal, a larger produce of wheat 

 would be obtained after a- bean than after a wheat crop, not- 

 withstanding its known dependence on the supply of nitrogen in 

 the soil. 



