116 Principles of Plant Culture. 



183. Evergreen Trees are sometimes Destroyed by Un- 

 timely Warm Weather in spring. ^Yith a soil so cool that 

 the roots are inactive, a sudden rise of atmospheric tem- 

 perature, espcially if accompanied by a drying wind, 

 may so far reduce the ^^ater in the leaves of evergreen 

 trees as to cause death of the foliage and even of the 

 trees themselves. This most frequently happens in the 

 seed-bed, in compact nursery plantations, or with recently - 

 transplanted evergreen trees. It is most disastrous on 

 poorly- drained clay soils that have a sunny exposure, 

 and at times when the ground is deeply frozen. 



The preventives to be observed are, a, means that will 

 prevent the tardy thawing of the ground, as thorough 

 drainage and not too t'lose planting; 6, means that will 

 prevent, in a measure, exposure to the sun, as planting 

 on a northern slope or shading the tiees (-tl4); c, means 

 that tend to prevent the deep freezing of the soil, as pro- 

 viding wind breaks which tend to retain the snow (204). 



184. A Temperature of 122° F. is Fatal to the Protoplasm 

 of most land plants. Afiuatic plants and the more 

 watery parts of land plants perish at a somewhat lower 

 temperatui'e. AVatery fruits, as tomatoes and gooseber- 

 ries, and the younger lea^'es of deciduous trees, are some- 

 times destroyed by full exposure to the sun's rays in 

 very warm weather. An occasional sprinkling of the 

 plants and of the soil about them will usually prevent 

 this result. 



185. Plants Under Glass should Not be Sprinkled in 

 Bright Sunshine. Drops of water upon the leaves of 

 plants often act as lenses in converging the rays of the 

 siui, and in a closed greenhouse or hotbed may cause a 



