58 



THE PRACTICAL GARDENER 



these can be conveniently got, thin turf laid with the gi-een side 

 undermost will be an excellent substitute. 



The season best calculated for the process of draining is 

 either late in autumn or early in spring, at which periods, the 

 springs are high ; the probability, therefore, of detecting their 

 course is then more likely to be attained than at any other 

 period during summer, when the quantity of water will be 

 lessened by evaporation, or during the winter months, when 

 the springs also become low or are impeded by the frost. 



CHAP, V. 



SYSTEMATIC ALTERNATION OF CROPS. 



In the cultivation of the ground, either in farming or gar- 

 dening, a proper attention to the regular rotation of crops 

 forms one of the first and principal features of good manage- 

 ment, although its beneficial influence has not yet been fully 

 accounted for by chymists. The rationale of rotation is thus 

 given by Sir Humphry Davy : " It is a great advantage in the 

 convertable systems of cultivation, that the whole of the manure 

 be employed ; and that those parts of it, which are not fitted for 

 one crop, remain as nourishment for another. Thus, if the 

 turnip be the first in order of succession, this crop manured 

 with recent dung immediately finds sufficient soluble matter for 

 its nourishment, and the heat produced by fermentation assists 

 the germination of the seed, and the growth of the plant. If 

 after turnips, barley with grass-seed be sown, then the land 

 being but little exhausted by the turnip crop, affords the 

 soluble parts of the decomposing manure to the grain. The 

 grasses, rye-grass, and clover remain, which derive a small 

 part only of their organized matter from the soil, and probably 

 consume the gypsum in the manure, which would be useless to 

 other crops; these plants, likewise, by their large system of 



