UNFAVORABLE TEMPERATURE 



111 



tomatoes and gooseberries, and the younger leaves of 

 deciduous trees, are sometimes destroyed by exposure to 

 the sun's rays in hot weather. An 

 occasional sprinkling of the plants 

 and of the soil about them will usu- 

 ally prevent this result. 



184. Sprinkling in sunshine. — 

 Plants under glass should not be 

 sprinkled in bright sunshine. 

 Drops of water upon the leaves of 

 plants often act as lenses in con- 

 verging 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 the brown spots so 

 often observed upon the leaves of 

 indoor plants that have been 

 sprinkled in bright sunlight, but 

 some of it may be due to inequali- 

 ties in the glass panes. Sometimes, 

 but rarely, this trouble occurs in 

 the open air. 



185. Sun-scald is the term ap- 

 plied to an affection of the trunk 

 and larger branches of certain not 

 quite hardy trees, usually upon 

 the south or southwest side, in 

 which the bark and cambium layer 

 (68) are more or less injured (Fig. 

 58). In severe cases, the cambium 



is totally destroyed, and the loosened bark splits longi- 

 tudinally or becomes detached. The effect is apparently 



Fig. 58. — Showing 

 effects of sun-soald on 

 trunk and , branches 

 of silver maple tree, 

 Acer dasycarpum. 



