1^42 MESSRS. J. B. LAWES, J. H. GILBERT, AND M. T. MASTERS, 
grasses overcoming it where the larger quantity of ammonia was employed. This was 
especially the case in the later years. 
In only one instance did it yield more than 20 per cent, of the total produce, and 
then it was with the mixed mineral manure and the smaller quantity of ammonia- 
salts. On each of the nitrate plots, on the other hand, it occurred in only insignificant 
amount. 
Comparison between the two species of Poa. —From what has been said of the two 
species of this genus, it is evident that the stolon-bearing Poa pratensis is specially 
benefited by nitrogenous manure in the form of ammonia-salts (in combination with 
mineral manure), hut not at all by nitrate of soda; whereas the more finely rooted and 
non-stoloniferous Poa trivialis has declined markedly on the ammonia plots, but has 
remained very prominent on the nitrate plots, especially where the larger amount of 
nitrate was used with the mixed mineral manure. This is strikingly illustrated in 
the following summary table, giving side by side the percentage (in the total produce) 
of each of the two Poas on two comparable plots; plot 9 with mineral manure and 
nitrogen as ammonia-salts, and plot 14 with the same mineral manure and the same 
amount of nitrogen, but as nitrate of soda. It may be added that there is the same 
contrasted tendency of the two species to increase or decrease respectively on the 
other ammonia and nitrate plots of the series. 
Table XLYI. 
Separation 
years. 
Plot 9. 
Mineral Manure and 
Ammonia Salts. 
Plot 14. 
Mineral Manure and 
Nitrate of Soda. 
Pea pratensis. 
Poa trivialis. 
Poa pratensis. 
Poa trivialis. 
Ter cent. 
Per cent. 
Per cent. 
Per cent. 
1862 
10-68 
8-72 
1-45 
22-48 
1867 
13-02 
2-14 
1-05 
32-93 
1872 
22-67 
0-64 
2-57 
24-76 
1877 
18-03 
0-11 
4-01 
21-59 
The interesting question arises whether the relatively shallow-rooting Poa trivialis 
predominates on the nitrate plots by reason of its fine surface roots arresting and taking 
up the nitrate before it has had time to penetrate too deeply. This view is favoured 
by the fact of the rapid growth which this plant invariably makes upon the application 
of the nitrate of soda in the spring. Another point worthy of remark is the contrast 
observable on plot 14, between the shallow-rooted Poa trivialis and the deeper and 
wiry-rooted Bromus mollis. In moist seasons, when the latter is relatively deficient, 
Poa trivialis is luxuriant, and vice versd. 
