As r 



FROZKN PLANT-ORGANS. 497 



As regards extreme winter-cold the following somewhat 

 different scale applies : 



i. VERY FROST-TENDER SPECIES. 



Sweet chestnut, plane, walnut, many fruit trees, such as 

 apricot, peach, quince and cherry.* 



ii. SOMEWHAT FROST-TENDER SPECIES. 



Pedunculate and sessile oaks, ash, elms, beech, robinia, 

 silver-fir, yew. 



Frost-hardy Species. 



Maples, horse-chestnut, lime, poplars, willows, hornbeam, 

 birch, alders, Pyrus sp., hazel; spruce, Scots, Weymouth, 

 Mountain and Cembran pines, larch, juniper. 



Pyramidal poplar is the least hardy of the poplars, rowan 

 least hardy of 'the Pyrus sp. The Weymouth pine may send 

 out second shoots in summer, which are usually killed in 

 autumn or winter. 



As regards the susceptibility of exotic trees that have been 

 introduced into Central Europe, the following experience has 

 been gained in Germany : 



A. Susceptibility of Exotic Trees to Late and Early Frost. 



i. VERY FROST-TENDER SPECIES. 



Black walnut, all hickories, Turkey oak ; Abies Nordman- 

 niana, Spach. (Caucasus), Douglas fir, Jeffrey's pine, Pinus 

 ponderosa, Laws. 



Black walnut is slightly less susceptible than common 

 walnut. Carya amara, Nutt, is the hardiest hickory. Nord- 

 mann's fir, sprouting late, is less susceptible than common 

 silver-fir. 



ii. FROST-TENDER SPECIES. 



American ash, grey walnut (Juglans cinerea, L.), sugar maple, 

 Calif ornian maple (A. circinatum, Pursh.) ; Sitka (or Menzies) 

 spruce, Corsican pine, Japanese larch. 



* Apricots and peach trees are killed by 26 30 C., walnut by 30 32 C., 

 the cherry-tree by 31 32 C. 



F.P. K K 



