1?0 PERMANENT NT7ESEEIES. 



the ditch serves not only to drain off with sufficient rapidity atiy' 

 excess of moisture in the soil of the nursery itself, but carries off 

 all the surface drainage of the higher ground outside. Indeed, 

 when the fall of the ground does not exceed about 1 in 20, the 

 mound alone is so effective that it is common to see large fields 

 as it were walled off by mounds of mere earth into a number of 

 very nearly level compartments. Any slight difference of level 

 that exists is soon corrected by rain, and the compartments then 

 form a succession of low terraces with earthen parapets. 



In the hills, the terraces should be given a slight slope inwards : 

 the rain Caught by each terrace will then drain away, partly 

 through the soil and out by the retaining wall, and partly by way 

 of the irrigation channels, without causing any risk of erosion to 

 the edge of the terrace. The rain falling on the slopes above, if at 

 all considerable, should be diverted, by means of one or more 

 channels, into the nearest ravine or gully. 



If due care has been exercised in the choice of the nursery site, 

 special drainage works will hardly ever be necessary. In the rare 

 event of their being required, the directions given in the next Chap- 

 ter for the construction of drains would generally apply. 



The next thing to do, after clearing and levelling the ground 

 and protecting it against erosion, is to free the soil of all its larger 

 coarse elements down to a depth of at least 18 inches, so that 

 it may contain nothing to blunt the sharp implements of thfe 

 nurseryman or overheat the soil, and also acquire a uniform texture. 

 The stones lying on the surface ought to be at once picked off, 

 those below the surface being got rid off during the progress 

 «f the actual tillage. Where the stony element is at all abundant, 

 some of it will still remain even after the tillage operations have 

 been completed, and will have to be removed by sifting or screen- 

 ing when the nursery beds and lines come to be prepared, as 

 explained further on. 



Lastly, we have to consider the tillage or real preparation of 

 the soil, the object of which is to remove and kill the roots of all 

 existing growth and to loosen and comminute and otherwise 

 improve the layer of the soil in which the future plants are to be 

 nourished. But in thus breaking up the soil, care must bc taken 

 to bring up to the surface as little as possible of the under-layers^ 

 which have never yet been exposed to fertilising weather influences. 

 By keeeping at the top all the richer portions of the soil, the lower 

 layers get the full benefit of the soluble substances of plant-food 

 carried down from them by rain or irrigation water; whereas if 



