49 vS PROTECTION AGAINST FROSt. 



iii. FKOST-HAKPY SPECIES. 



Canadian poplar, cherry birch (Betula lenta, L.), white 

 spruce, Pinus rigida. Mill (pitch pine), Lawson's cypress, 

 Sequoia Wetting tonia t Seem., red cedar (Juniper us rinjun- 

 ana, L.). 



Young seedlings of pitch pine are occasionally killed by 

 early frosts. Lawson's cypress and Wellingtonia are somewhat 

 susceptible to frost for the first 4 5 years. 



B. Susceptibility of Exotic Species to Winter-Frost. 

 It appears useless to give Hess' list of delicate species, as it 

 includes some plants that are quite hardy in the British Isles. 



Frost-hardy Species. 



Ked oak, ashleaved maple, sugar maple, American ash, all 

 hickories, cherry birch, Canadian poplar, Nordmann's fir, 

 Balsam fir, Douglas fir, Sitka spruce, white spruce, Pinus 

 ponderosa, Laws., Japanese larch, Lawson's cypress, Welling- 

 tonia, red cedar. 



From these lists, it appears that the introduced exotics 

 hardly suffer more from frost than indigenous species. Several 

 species not mentioned by Hess, such as Thuja gigantea, Nut- 

 tall (T. plicata, D. Don., according to Sargent), Taxodium 

 distichum, Kich., are frost-hardy in Britain. In the west of 

 the British Isles numerous species thrive, which cannot with- 

 stand the frosts of Central Europe, or even of the eastern 

 counties of Great Britain. 



c. Part of Tree. 



The inflorescence, opening leaves and young shoots suffer 

 most ; the developed leaves and needles less, and least of all 

 the buds. In silver-fir and spruce the damage is nearly 

 always confined to the spring-shoots, the old needles escape, 

 and as in the silver-fir the terminal buds open out later than 

 the lateral buds, the latter are more often frozen. 



d. System of Management. 



Coppice, especially with short rotations, suffers more than 

 high-forest, as the susceptible young growth occurs so 



