Plants as Affected by Heat. III 
183. Evergreen Trees are sometimes Destroyed by 
Untimely Warm Weather in spring. With a soil so cool 
that the roots are inactive, a sudden rise of atmospheric 
temperature, especially if accompanied by a drying wind, 
may so far reduce the water in the leaves of evergreen trees 
as to cause death of the foliage, and even of the trees them- 
selves. 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 southwesterly 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 close planting; b, means that will pre- 
vent, in a measure, exposure to the sun, as planting on a 
northern slope, or shading the trees (414); c, means that 
tend to prevent the deep freezing of the soil, as providing 
wind breaks (204), which tend to retain the snow. 
184. A Temperature of 122° F. is Fatal to the 
Protoplasm of most land plants. Aquatic plants, and the 
more watery parts of land plants, perish at a somewhat 
lower temperature. Watery fruits, as tomatoes and goose- 
berries, and the younger leaves of deciduous trees, are 
sometimes 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 sun, 
and, in a closed greenhouse or hotbed, may cause a heat 
that is fatal to the foliage beneath them. This may explain 
