100 J. H. Gilbert -Points in connection with Vegetation. 



the amount of it referred to the different orders is calculated 

 upon their percentage determined in six years only, four of 

 which are among the last five, and the fluctuation according 

 to season is in some cases very considerable, while in others there 

 is a progression in the changes, which render an accurate 

 estimate of the average botanical composition of the herbage 

 over the whole period impossible. The figures do, however, 

 undoubtedly represent the truth sufficiently nearly for our 

 present purpose. But before referring to the yield of nitrogen, 

 it may be remarked, in passing, how much greater is the 

 increase of gramineous produce by the use of purely mineral 

 manures in this mixed herbage than in the case of gramineous 

 crops grown separately. The interesting question arises, how 

 far the result is due to the direct action of the mineral manures 

 in enabling the grasses to form much more stem and seed — 

 that is, the better to manure — which, as a matter of fact, they 

 are found to do? or how far the increased growth is to be 

 explained by an increased accumulation of combined nitrogen 

 available for the grasses in the upper layers of the soil, as the 

 result of the increased growth of the Leguminosse induced by 

 the potass-manure, as already illustrated by the results obtained 

 in alternating clover and barley, and in an actual course of 



Eeferring to the yield of nitrogen, it is seen that, without 

 manure, it has diminished during the last as compared with 

 the first ten years ; but that the average is thirty-three pounds 

 per acre, per annum, or considerably more than with a gramin- 

 eous crop grown separately. 



With super-phosphate of lime alone, the yield of nitrogen 

 over the first ten, the second ten, and the twenty years, is very 

 nearly the same as without manure. It is slightly higher as 

 is also the total amount of produce; but while the quantity 

 contributed by gramineous species is rather more, that yielded 

 by leguminous species is less, and that bv species belonging to 

 Other orders more than without manure. 



With super-phosphate of lime, and sulphates of potass, soda 

 and magnesia, during the first six years, but no potass during 

 the last fourteen years (plot 8), the amount of both gramineous 

 and leguminous herbage is very much increased; ami that of 

 the leguminous produce was especially so during the earlier 

 years. The result is a yield of 55*4 lbs. of nitrogen per acre, 

 per annum, over the first ten years, of only 381 lbs. over the 

 second ten years, and of 46'3 lbs. over the twenty years. 



With the complex mineral manure, including potass each 

 year throughout the period of twenty years (plot 7), legumi- 

 nous species contribute about one-fifth of the whole produce, 

 or very much more than in either of the other cases. The 



