DISCRIMINATIVE TREATMENT OF SURFACES. 253 



On ground with a flat surface, and soil of a uniform 

 quality^ a combined botanical and pictorial grouping of 

 the whole collection will be the principal object of study. 

 Certain shrubs will require special soils, such as peat and 

 sand, and these should be formed for them. Where 

 there is a considerable diversity of surfaces and soils, 

 attention ought to be directed not only to the grouping 

 on the principles already indicated, but also to the etfect 

 of the proposed distribution in relation to the surface 

 which is to be covered, and to the soils on which the 

 plants are to grow. We must consider what group will 

 appear to most advantage on a given hill, or knoll, or 

 slope, or hollow, and whether also the soils of these may 

 not be more suitable for one order or family than for 

 another. A fine hollow with moist soil might seem, at 

 first sight, to promise a propitious site for willows, alders, 

 and poplars, and yet on examination it may be found that 

 such locality may be better adapted, both in reference to 

 beauty and luxuriance of growth, for the hardier sorts of 

 what are usually called American shrubs. On the other 

 hand it may be ascertained, with some degree of cer- 

 tainty, that the low damp space referred to would prove 

 injurious to the more tender pines, cistus, magnolias, 

 and arbutus. The diversities of climate arising from 

 difierences in exposm-e and evaporation, even within the 

 limited space of a dozen acres, is often very considerable. 

 We are aware that to attend properly to these and si- 

 milar considerations is no easy matter, but they do not 

 on that account lose their importance ; and they should, 

 if possible, receive the attention which is due to them. 



In an arboretum arranged on strictly botanical prin- 

 ciples, there is an invariable deficiency of the efiect pro- 

 duced by evergreen trees, as these valuable means of 



