SCIENTIFIC FARMING AT ROTHAMSTED. 87 



experiments to determine the differences in the amount and constitu- 

 ents assimilated by plants of different botanical families, under similar 

 conditions, and of the same plant under varying conditions. From 

 these investigations, so far as they have been published, it appears 

 that the chemical relations of the plant and soil are, to a great extent, 

 determined by botanical and physiological conditions. 



In the experiments with the mixed herbage of "permanent meadow," 

 for example, it was noticed, even in the first years of the experiments, 

 that " those manures which are most effective with wheat, barley, or 

 oats grown on arable land that is, with the gramineous species grown 

 separately were also the most effective in bringing forward the grasses 

 proper in the mixed herbage ; and again, those manures which were 

 the most beneficial to beans or clover, most developed the leguminous 

 species of the mixed herbage, and vice versa.'''' 



In the produce grown continuously without manure the average 

 number of species was forty-nine. Of these seventeen are grasses, 

 four leguminous species, and twenty-three of other orders. By weight 

 the grasses averaged sixty-eight per cent, leguminous species nine per 

 cent, and species of other orders twenty- three per cent. 



In the produce of the plot most heavily manured and yielding the 

 heaviest crops, the average number of species was nineteen ; of which 

 twelve to thirteen were grasses, one only (or none) leguminous, and 

 five or six only of other species. By weight the grasses averaged 

 about ninety-five per cent, the leguminous species less than O'Ol per 

 cent, and other orders less than five per cent. 



On the plot receiving annually manures that are of little avail for 

 gramineous crops grown separately in rotation, but which favor beans 

 or clover so grown, the average number of species was forty-three, 

 of which seventeen were grasses, four leguminous, and twenty-two 

 belonging to other orders. But by weight the grasses averaged but 

 from sixty-five to seventy per cent, the leguminous species nearly 

 twenty per cent, and all other species less than fifteen per cent. 



The " struggle for existence " and the " survival of the fittest," 

 therefore, determine the character of the species contained in the 

 produce under the conditions, and the chemical composition of the 

 crop varies accordingly. With an increase of the leguminous produce 

 the nitrogenous constituents are increased, and with a decrease in the 

 leguminous produce the nitrogenous constituents are diminished. 



Experiments with leguminous, gramineous, and other families of 

 plants were made for several years in succession, at Rothamsted, to 

 determine whether plants assimilate free or uncombined nitrogen. 



The relations of nitrogen to the growing plant and to the soil and 

 the sources of the nitrogen of vegetation have been prominent subjects 

 of investigation in all the Rothamsted field-experiments. 



It is not my purpose, in this connection, to discuss the various the- 

 ories of vegetable growth, or to give an account of the many contro- 



