THE FOREST NURSERY 349 



of the beds during dry periods. Dense stands of seedlings exhaust 

 the soil moisture very rapidly; hence, close watch must be kept 

 over the seedbeds during dry periods, and if the soil about the roots 

 of the seedlings becomes overdry a thorough moistening to the 

 depth of root penetration is essential. 



Winter killing is the death of the whole or part of the plant as 

 a result of the top drying when the soil and roots are frozen. The 

 water given off by the top cannot be replaced by absorption from 

 the soil. Sudden periods of warm weather in the midst of cold 

 winter weather cause the most damage. Trees affected by winter 

 killing in the seedbeds and transplant beds have the same general 

 appearance as those affected by sun scorch. The damage is great- 

 est during winters with low temperature and little snow. It can be 

 prevented by protecting the nursery by windbreaks and by mulch- 

 ing the beds during the winter. 



Winter molding or mulch injury sometimes results from a heavy 

 fall of snow which remains over the beds until late in the spring, 

 or from a heavy mulch of leaves or other material which packs 

 down over the seedlings and is not removed sufficiently early. 

 The damage appears to be due to the plants not being exposed to 

 the sun and air early in the spring rather than to the character 

 and quantity of covering during midwinter. In regions of heavy 

 snowfall when the snow comes early and lasts until late in the 

 spring the artificial mulching of nursery beds is unnecessary; the 

 snow is a good mulch in itself. When a heavy mulch of leaves 

 or like material is applied and is followed by a heavy fall of snow 

 which continues throughout the winter and early spring, there is 

 almost always considerable loss from molding. No more mulch 

 should be used than necessary to provide protection from the sun 

 and only loose, light material should be used. It should be re- 

 moved during the first warm days of spring. When winter mold- 

 ing or mulch injury has occurred in coniferous seedbeds the leaves 

 turn brown and fall from the plants soon after they are uncovered. 

 The terminal bud is almost always severely injured or destroyed. 

 Even in cases where all the leaves are killed the roots remain 

 healthy. 



Ebermeyer l describes a blight which sometimes occurs in conif- 

 erous nurseries due to a sudden period of warm weather in early 



1 Ebermeyer, E. W. F.: Die physikalischen Einwirkungen des Waldes auf 

 Luft und Boden. S. 251. Aschaffenburg, 1873. 



