SCIENTIFIC TREATMENT. 



233 



descriptions of the species. Any hardy plants recently 

 introduced may easily be inserted into their proper 

 places as soon as their respective genera and orders are 

 ascertained. 



In connection with the genera we have indicated 

 whether the individuals are trees or shrubs^ whether 

 they are deciduous or evergreen^ or whether they are 

 partly the one and the other. When the genus is not 

 generally hardy^ it is marked as sub-hardy ; and when 

 there are hardy and sub-hardy species in cultivation^ 

 this fact also is marked. Where no such distinction is 

 made, the plants may be considered as hardy in the 

 average climate of the United Kingdom. The heights 

 specified must be regarded as the general altitude of the 

 genus rather than the stature of the individual species ; 

 the latter being often extremely varied, in some cases 

 ranging towards the higher, in others towards the lower 

 limit. The numbers of species and varieties are some- 

 times only approximative. Mr. Loudon, for example, 

 describes 170 willows, while we have marked only 100; 

 and even that lower number it would probably be diffi- 

 cult to procure. We beheve that there are about 1500 

 species and 1000 botanical varieties of hardy trees and 

 shrubs — exclusive of what may be called florists' va- 

 rieties of roses, azaleas, etc. — cultivated in our weU- 

 appointed nurseries. Of course, a selection of these is 

 sometimes all that the extent of the ground to be occu- 

 pied will permit to be employed. 



As many of Dr. Lindley's alliances and orders do not 

 contain plants which are ligneous and hardy, they are of 

 course omitted. Tor the sake of convenience we have 

 marked the alliances and orders, selected for our present 

 purpose, with running numbers, beginning in both cases 



