THE NITROGEN SUPPLY. 409 



In the adjoining field, which is under experiment with 

 j)ermanent barley, potatoes, and leguminous crops, I planted 

 about a hundred seeds, placing three together, and allowing 

 them the space of a square yard or more from which to col- 

 lect their food. 



The plot of ground upon which they were planted is out- 

 side the portion of the field under experiment : it certainly 

 has received no dung for the last thirty years, and may be 

 described as a piece of waste land which has been ploughed 

 with the rest of the field, but has not been cropped, though 

 vegetation has sprung up principally in the form of thistles 

 or annual weeds. 



My object in sowing the corn was a very simple one : I 

 wished to ascertain whether the color of the plant, under 

 different foods, corresponded with that of the various cereal 

 crops which we have under experiment. 



At the period at which I am writing (Aug. 22) the corn 

 upon the unmanured wheat-land is only one foot high : there 

 is no leaf that is one inch in width, and the color is yellow, 

 or a yellowish-green. 



In the adjoining field some of the plants are between four 

 and five feet high, while the leaves are three inches and a 

 quarter wide, and of a very dark, rich green : other plants, 

 although growing and luxuriant, are much paler in color. 

 In this field I have used mineral manures alone, and mineral 

 manures with nitrates. 



In the same field with the corn, and close to it, there are 

 fifteen different sorts of leguminous crops growing : they are 

 all manured with (1) various mineral manures alone, and (2) 

 with the same minerals, and, in addition, nitrates or salts of 

 ammonia. 



Here we have no changes in the color of the plants due to 

 the influence of the various manures : there are none of those 

 varieties of tint, from a yellowish-green to a greenish-blue 

 (which in the evening appears almost black), that we find jn 

 some of our graminaceous crops under experiment. A prac- 

 tised eye might detect, in some cases, a brighter and more 

 healthy green ; but that is all. 



So far as the corn is concerned, by a comparison of the 

 produce grown on the permanently unmanured land with 

 that grown on the field supplied with minerals, and nitrates 



