38 INVESTIGATION INTO THE AMOUNT OF WATER 



VI. — Experimental Investigation into the Amount of Water 

 given off by Plants during their Growth ; especially in rela- 

 tion to the Fixation and Source of their various Constituents. 

 By J. B. Lawes, of Rothamstead. 



(Communicated December 4, 1849.) 



Of the several natural orders of plants which yield food to man, 

 or to the animals destined for his consumption, or other use, per- 

 haps the most important, both as to the extent of their distribu- 

 tion and the amount of the products they supply, are the Gra- 

 minacecB and the Leguminosce. There are others, however, to 

 which we are indebted for the roots and tubers, the extended 

 cultivation of which, in alternation with corn, so prominently 

 characterises at least the national agriculture of the present day. 

 The corn-plants of most extended utility in the Leguminous 

 family are the Bean and the Pea ; but we owe to it also some 

 of the most important of our fodder-plants, such as Clover, Tre- 

 foil, Vetches, and others. The Graminaceous family, on the 

 other hand, supplies us with Wheat, Barley, Rye, Oats, Mice, 

 Maize, the Sugar Cane, and others, besides the natural grasses 

 of our meadows and pastures. 



Between these two great natural orders of plants there are, 

 however, many striking and obvious points of contrast as to 

 habits, structure, and products, whilst the vastly different posi- 

 tions allotted by experience to the individuals which they respec- 

 tively comprise in a system of alternate cropping are such as 

 clearly to indicate that the resources of their growth are also 

 widely different ; and it has been maintained that an explanation 

 of them is mainly to be found in the various mineral composition 

 of the crops. The scattered observations, however, of many ex- 

 perimenters, and some of not very recent date, would seem to 

 favour an opposite view of the question, and the vastly accumu- 

 lating published results of the last few years lend an ample con- 

 firmation in the same direction. 



For our own part, an extensive and systematic series of experi- 

 ments, conducted both in the field and in the laboratory, leaves 

 not a doubt in our mind that in the ordinary practice of agricul- 

 ture in Great Britain the exhaustion which is suffered is promi- 

 nently connected with a deficiency of " organic " or primarily 

 atmospheric, rather than the "mineral" or, more properly, 

 soi'Z-constituents ; and especially that the supply of nitrogen, 

 relatively to other constituents, is defective. We have already, 

 in the Journal of the Royal Agricultural Society, indicated some 

 striking facts bearing upon this point, in the discussion of the 

 results of some of our experiments upon the growth and composi- 

 tion of Wheat and of Turnips. Beans, Peas, and Clover, as the 



