FROZEN PLANT-ORGANS. 495 



an inspection of a cross-section of a stem. Frost also causes 

 certain forms of canker in broadleaved trees. 



The physiological effects of severe winter-frost consist chiefly 

 in killing wood which is not fully ripe, and which has been 

 spared by the early frosts. In this way, either the youngest 

 shoots, the autumnal woody zone, or the whole annual ring of 

 wood inside the cambium-zone may suffer and cause cup-shake 

 in wood. Where cup-shake is thus caused, the concentrated 

 sap in the cambium-zone preserves it from damage, while the 

 zone of the sapwood next to it becomes so dried by the freez- 

 ing of the sap within it as to separate partially or entirely 

 from the cambium. Mechanical injuries done by winter-frost 

 will be described further on. 



The damage done under the headings: species, tree-part, 

 system of management, age, locality, soil-covering, density of 

 stock, and weather will each be considered separately. 



1. Species of Tree. 



As a rule, broadleaved trees are more susceptible, to frost 

 than conifers, and species which prevail in the south suffer 

 more than those from the north. As special conditions affect- 

 ing the extent of the damage done by frost, the degree of 

 development and power of recovery of the plant are important. 

 Thus the beech and oak are equally liable to injury by frost, 

 .but the oak suffers less than the beech, as it shoots out later 

 in the spring. . 



As regards recovery from damage, the oak is also more 

 favoured than the beech, for if its leader be frozen, lateral 

 buds develop new leaders, but the beech having fewer dormant 

 buds cannot do this so well. The oak can also put out a 

 second foliage during the year if the first be frozen, but the 

 beech cannot. Hence wood-formation is less hindered in the 

 oak than in the beech. Similar considerations affect other 

 species. As regards conifers indigenous in Central Europe, 

 the . silver-fir is most susceptible, but I have had a bed of 

 yearling silver-fir at Coopers Hill, quite unprotected during 

 the winter 1902-3, and planted them out safely under cover in 

 spring. Older silver-fir in the nursery had their young shoots 

 severely frozen in the spring. 



