Relation of Weather to Crops 49 



temperature of the atmosphere over or about the exposed objects, 

 and that over or about the shaded objects. Shutting off or admit- 

 ting sunlight, therefore, has a double effect upon plants. 



During weather too cool for the normal growth of a plant, direct 

 sunshine promotes its activities and results in benefit, while shade 

 has the opposite effect. The almost continuous bright sunshine of 

 our winters is, therefore, a distinct advantage to vegetation and 

 results in more rapid growth than could take place in a cloudy region 

 where other conditions (both of soil and of weather) are the same. 

 It has the effect, however, of unduly warming during the day decidu- 

 ous trees in their leafless condition and causing some of them to 

 bloom so early some years as to receive injury from frost. 



During the warm portion of the year, parts of many plants 

 become overheated in direct sunshine and injury to tissue results. 

 This is especially true of the trunks of fruit trees which are exposed 

 to the sun on the southwest side. Sometimes fruits, such as oranges, 

 for example, will become sunburned and stunted in growth by 

 exposure to the direct rays of the sun. Occasional injury to the 

 leave's may occur, but injury to the stem is far more serious. More- 

 over, since the leaves are continually being cooled more or less by 

 the evaporatiion of moisture from their tissues, they do not become 

 as highly heated as do stems and tree trunks from which very little 

 evaporation is taking place. Hence, plants with heavy foliage 

 that shades the other parts have a distinct advantage, other things 

 being equal, over ones with slight foliage, provided they are supplied 

 with sufficient water. 



Not only does insufficient or improperly located foliage result 

 in the overheating of exposed stems and other pjarts, but the soil 

 immediately about the plants becomes so highly heated as not only 

 to seriously injure shallow roots but to radiate heat so rapidly that 

 the effect of the direct rays of the sun is thereby much augmented. 

 For two reasons, therefore, it is important that varieties of fruits, 

 vegetables, and other crops be selected having a heavy foliage not 

 sensitive to heat and that trees and shrubs be headed low. Pro- 

 tection to st^ms or trunks, to roots, and to the maturing crop of 

 fruit or vegetables is thus secured. 



Similar results are also obtained by close planting of vegetables, 

 one plant thus shading its neighbor and all shading the soil. The 

 crops for which such precautions are important are such as peas, 

 beans, tomatoes, squashes, melons, and strawlerries. 



