98 PLANT LIFE ON THE FARM. 



of the manure employed. They vary somewhat in robust- 

 ness of constitution and ability to withstand frost or 

 drought; and their structural characters are generally 

 speaking characteristically different from those of other 

 plants, and variable as between species and species. Some 

 maintain their ground or even increase when growing in 

 competition or association with their fellows ; others such 

 as Anthoxanthum odoratum, Festuca ovina, and Agrostis 

 vulgaris can only hold their own or assert themselves when 

 the competition exercised by their associates is relatively 

 weak, and succumb under the opposite circumstances. 



The grasses, both in number of species and in relative 

 and actual amount of produce, exceed the plants of all other 

 orders. The lowest produce occurs on the continuously 

 unmanured plots ; the highest on those to which a highly 

 nitrogenous manure, such as ammonia salts or nitrate of 

 soda, is continuously applied in combination with earthy and 

 alkaline salts especially potash. But while the total gra- 

 mineous produce is thus increased by the description of 

 manure just mentioned, the number of species of grass is 

 reduced. On the unmanured plots, on the average, 16 

 different sorts of grasses may be found, each contributing 

 a fair proportion to the total herbage ; 13 only are found on 

 the highly ammoniated plots, and of these only a very few 

 contribute materially to the crop, the remainder being 

 present in such small quantities as to make but little 

 difference in the totals. 



The principal external characteristics which favour the 

 growth of the grasses in their competition with other plants 

 are their dense root-growth, monopolising as it were all the 

 soil within reach, and affording little power to the roots of 

 other plants to penetrate the mass. To an extent variable 



