48 BEGINNER'S BOOK OF GARDENING 



state of nature they often appear to be growing on the 

 very surface of the rock itself, yet if we break away a 

 part of the rock on whose surface they appear to be 

 rooted, we shall find there rootlets penetrating for 

 inches, often for feet, through minute cracks and crevices 

 scarcely visible to the eye. As a rule, Alpines do not 

 require rich soil, but depth of soil they must have. 

 Only in this way are they able to be afforded that uni- 

 formity of temperature which is one of the essentials of 

 their existence. Three feet deep is not too much for 

 most kinds of Alpine plants, and for the majority of 

 species this soil should consist of a mixture of loam, 

 sand, leaf mould, peat, and broken grit. Indeed, the 

 most satisfactory type of rock garden for a small area 

 is to construct what is practically a slightly raised border 

 almost buried in which are placed irregular masses of 

 local rock. Only rough pieces of stone, preferably the 

 stone of the locality, should be used. Limestone and 

 sandstone are especially suitable. Burnt bricks, burrs, 

 and shells should be carefully avoided. The pieces of 

 stone should, as we have said, be almost buried in the 

 soil, and the projecting parts should appear to be a 

 natural outcrop of stone. In any case a rockery should 

 be broad and with little exposure at the sides ; not high 

 and pointed, as except in the case of a few plants the 

 more exposure to the sun the better. Good drainage is 

 essential, and this is one of the reasons why a rock 

 garden should be raised somewhat above the general 

 level of the surrounding ground. At the same time 

 there must be no hollows in the middle of the rock 

 garden, or the plant roots will be dried up. There 

 must also be facilities for an efficient supply of water 

 thritughout the summer months. It is a good plan to 

 mix with the soil a good proportion of grit or coarse 

 sandstone, some growers even using as much as one half. 

 The tendency to " damp off" in winter, which is the 



