INJURIES DUE TO ATMOSPHERIC INFLUENCES 291 



injurious effects manifest themselves in a variety of ways which 

 have not hitherto been sufficiently investigated. After very 

 severe and long-continued winter cold, the cortex, bast, and 

 cambium, and the wood-parenchyma as well, die and become 

 brown, The trees either fail to produce leaves in the following 

 season, or if they do bear leaves, flowers, and even fruit they 

 wither up entirely in the course of the summer or autumn. As 

 the wood does not lose its power of conducting water all at once, 

 trees that are injured by frost may be able to produce leaves. 

 The power, however, disappears as decomposition spreads from 

 the parenchymatous cells to the conducting organs, or as the 

 wood dries up from without inwards. Sometimes the cortex 

 and bast are only killed in patches, and when this is the case a 

 callus may gradually form over the damaged parts. 



It sometimes happens, especially in the case of exotic conifers, 

 occasionally also in dicotyledons, that the cortex, bast, cambium, 

 and frequently also the youngest annual wood-rings exhibit 

 immunity from frost ; the wood-parenchyma, especially that in 

 the neighbourhood of the medulla, being alone destroyed. In 

 such a case conifers usually die suddenly from drought in the 

 beginning of May ; whereas dicotyledons, whose cambium 

 becomes active during the bursting of the buds, frequently 

 remain alive. This result is due to the fact that the cambium 

 having remained unaffected, forms a new wood-ring before the 

 old frosted wood has lost its power of conducting sap ; or else 

 the youngest annual rings escape the frost and suffice for the 

 transference of the sap. Although the shoots and Leaves are but 

 poorly nourished for some years after the occurrence of the frost, 

 such trees ultimately recover. Under such circumstances it 

 often proves an excellent plan to prune severely, so as to bring 

 evaporation into proportion with the diminished quantity of 

 water that finds a passage through the wood. In very dry 

 years, however, many trees ultimately succumb to the after- 

 effects of the frost. 



When frost affects plants during the season of growth and 

 this is the case with late and early frosts a fatal issue no longer 

 depends on the hardiness of the plant, but upon the manner of 

 thawing. When in a state of vegetative inactivity, our indigenous 

 trees can withstand the most severe cold of winter with 



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