492 PROTPX'TIOX AGAIXST FROS'I'. 



ii. Splittinf; tlio stems of trees. 



iii. Causliif^ canker in stems of troes. 



iv. Tprootinf^ younp; plants. 



Section I. — Frozen Plant-Organs.* 

 1. External Appi'arancc of Injiirrd l*la)its. 



Frozen plants, or organs of plants, become soft, flexible and 

 hang down or wilt. When dead they eventually turn brown 

 or black. These outer signs result from the reduced tension 

 of the tissues injured by frost, and from their inability to fulfil 

 their proper functions. Foliage frequently falls prematurely 

 owing to early frosts, a film of ice forming at the base of the 

 petiole, as in robinia and elder, which may become leafless 

 in a few days, the fallen leaves remaining quite green and 

 apparently unaffected by the frost. In other trees, as horn- 

 beam, beech or oak, the frozen foliage may die and turn 

 brown, and remain on the tree until the buds swell in the 

 spring, the normal autumnal leaf-fall being prevented by the 

 fact that the leaf is killed before the usual layer of cork, which 

 causes defoliation, has formed at the base of the petiole. 



M. Mer relates ("Rev. des E. et F.," July, 1897, p. 424) 

 that in a frost in February, 1895, in the Hautes Yosges, near 

 the Lake of Longemer, young silver-fir attacked by frost did 

 not lose their lower branches, which were protected by snow, 

 while their middle branches, above the snow, were killed. 

 The buds of the two or three highest verticils remained 

 dormant for a year, producing no shoots in 1895, and some 

 of them not even in 189G, whilst the terminal bud produced a 

 leader in the summer succeeding the frost. Hence it appears 

 that organs may be aft'ected by frost, without being killed, 

 and that the most vigorous organs, such as terminal buds, 

 best resist frost. 



2. Kxidanation of the Action of Frost. 

 Death by freezing is usually caused by late frosts, less by 

 early frosts. Winter frost rarely kills indigenous plants. 



* Goppcrt, Dr. II. It., •• Ucber das Gefriercn, Erfricren der r(lanzc7i und 

 Scliiitziiiittel dii,i,regcii." Stuttpirt, 1SS3. 



