NATURAL AND ARTIFICIAL GRASSES. 189 



perennial, and are to be used as mowing lands or for 

 pasturage. The artificial grasses are more frequently 

 intended to occupy the ground for one or two years only 

 in the rotation with other crops, and are generally com 

 posed of only one or two species of plants, and those 

 annuals, or at most biennials. 



658. In this country it is common to sow one or more 

 species of clover with the natural grasses. The clover 

 then occupies the ground almost exclusively during the 

 first and sometimes the second year, but afterwards the 

 perennial grasses take its place and form a permanent turf. 



659. The natural grasses form a close turf or sward, 

 and when left uncut to be fed off by animals, this turf 

 makes what is called a pasture or pasturage. 



660. There are certain situations which must be 

 improved as pasturage, if at all. Such are steep slopes 

 on which cultivation is difficult or expensive, and where 

 the soil would be washed into the valleys below, if broken 

 up by the spade or plough ; also lands which lie along 

 the margins of streams or rivers liable to periodical 

 overflows, by which growing crops might be endangered 

 or the soil be washed away, and low marshy lands which 

 cannot be drained so as to produce annual crops. In 

 these latter situations, however, the wild grasses frequently 

 come in so luxuriantly, on account of the richness of the 

 soil, as to give good crops for hay for many years in 

 succession, without any cultivation whatever. 



661. There are great differences between the different 

 species of grasses. Some are short lived, others more 

 permanent ; some mature early, others later ; some 

 contain much nutriment, others little. The different 

 species require different kinds of soil also, and withdraw 

 from it different substances and elements. 



