496 PROTECTION AGAINST FROST. 



A classification of woody plants according to their suscepti- 

 bility to frost is not impossible, but can only be of local value, 

 as the earlier or later shooting out of a tree depends on the 

 altitude, as well as on the species grown. 



The following list groups trees according to their suscepti- 

 bility to late and early frosts : 



i. VERY FROST-TENDER SPECIES. 



Ash, walnut, plane, sweet chestnut, beech, oaks,* robinia 

 (early frosts), silver-fir. 



ii. MODERATELY FROST-TENDER SPECIES. 



Sycamore, Norway maple, Salix viminalis, L., spruce, larch, 

 cluster pine. In many localities, spruce suffers so severely as 

 to be placed in group i. 



iii. FROST-HARDY SI-ECIES. 



Hornbeam, elms, rowan, aspen, poplars, willows (except 

 S. viminalis, L.), alders, birches, horse-chestnut, limes, hazel; 

 Scots, Black, Weymouth, Cembran and mountain pines ; 

 juniper. 



In the case of very severe late frosts, species in the last 

 group, such as the Scots pine, may suffer, or be killed when 

 quite young. 



If the locality be taken into account, as sea-coast, flat, hilly, 

 or mountainous land, some modifications must be made in the 

 above groupings. 



In general, local trees which shoot out early are more or 

 less frost-hardy, for instance, the birch, alder, and sallow; 

 frost-tender species such as the oak and ash shoot out later in 

 the spring, and the beech, which shoots earlier than either, 

 owes its immunity from frost to its power of resisting cover 

 under which spring frosts do not occur. The faculty of pro- 

 ducing adventitious buds (oak and silver-fir) is helpful to those 

 species. 



The larch, which shoots out early in the spring, suffers in 

 low situations from late frost. 



* Some North American oaks and ash-trees suffer les$ th.an. European species ; 

 Turkey oak is less hardy than either. 



