60 Principles of Plant Culture. 



The area affected by a group of trees is often much 

 larger than is supposed. Fig. 26 shows how an ever- 

 green hedge may restrict the growth of corn in an ad- 

 joining field. We should not infer from this, however, 

 that trees are on the whole detrimental to agriculture. 

 They serve many useful purposes. 



Experimental crops intended to be comparable with 

 each other should not be planted near growing trees. 



76. The Brittleness of Young Plant Tissues depends 

 upon the degree of water pressure within the cells. 

 Foliage is usually most brittle during the morning and 

 least brittle during the latter part of the day, because 

 transpiration is most active during the warm hours 

 of the day. Lettuce and other salad plants are, there- 

 fore, apt to be more crisp and tender when cut in the 

 morning. Tobacco, in which breaking of the leaves is 

 harmful, is preferably cut in the afternoon. Young 

 hoed crops are generally less injured by the smoothing 

 harrow in the afternoon than in the morning, and grass 

 intended for hay usually dries soonest when cut in the 

 afternoon. Lawn grass generally cuts easier in the 

 morning than in the afternoon. 



Slightly withered vegetables may have their erispness 

 partially restored by soaking them in water for a time. 



77. The Evaporation Current. Since the water of 

 plants is taken in from the soil through the root-hairs 

 (100), and escapes more or less rapidly by transpiration 

 (74), it is clear that in leafy plants a current of water 

 must pass from the roots through the stem and branches 

 into the leaves, and that the rate of this current will 

 depend much upon the rate of transpiration from the 



