SHADE TREES. 147 



hemlock, pine and others are easily transplanted with little loss because 

 it is not difficult to obtain enough of the lateral root system to supply 

 the tree. Some species, however, possessing lateral root systems appear 

 to be dependent upon root fungi (micorhiza), which restricts them to 

 particular soils and renders them sometimes difficult to get established 

 in certain localities. Many plants, like the sumach and others, possess 

 long, creeping lateral roots which must be taken up carefully to insure 

 successful transplanting. 



Depth of Roots. 



Some idea of the depth to which roots extend may be had by examining 

 excavations near trees, and also to some extent by plowing. Most elm and 

 maple roots are confined within 2 feet of the surface, but in wet soil they are 

 generally much nearer than this. The large roots of the European larch 

 are very near the surface, and usually somewhat exposed. Pine and 

 hemlock roots are frequently seen running on top of the ground, and in 

 swamps, where trees often blow over, it may be observed that the entire 

 root system is located within a few inches of the surface. Oak and chest- 

 nut roots do not appear to penetrate very far, as shown by the ease with 

 which winds uproot the trees when growing even in ordinary soil. The 

 maximum number of roots of most trees in ordinary soil is probably 

 located between 1 foot and 18 inches below the surface. 



Roots often penetrate soil to great depths, and when growing in gravel 

 become flattened out in irregular shapes from growing around large 

 pebbles. Apple tree roots have been known to grow through a mass of 

 coarse gravel 8 feet to obtain water, and elm and rock maple roots will 

 penetrate quite a distance to reach a water table. The roots of the com- 

 mon clover one year old have been known to descend to a depth of 8 feet; 

 those of parsnip more than 13| feet; and of lucerne, a leguminous plant, 

 more than 20 feet. The roots of a leguminous tree growing in India have 

 been traced to 69 feet below the surface without reaching their full length. 



The distance to which roots extend laterally may generally be roughly 

 determined by the spread of the crown. Practically all trees extend their 

 roots beyond their foliage or branches. The Norway spruce and others, 

 which have narrow crowns, do not have an extended lateral system. The 

 maple and elm have well-developed root systems which extend to a con- 

 siderable distance. 



There is a correlation between the shape of the aerial portion of a 

 plant and its root system. The leaves of root crops like radish, turnip 

 and others are so placed on the stalk that they divert the rain toward the 

 axis of the plant, or taproot. On the other hand, the apices of the leaves 

 of many plants are deflected away from the axis, i.e., toward the lateral 

 or feeding roots. Most shade trees are noted for their large crowns, with 

 the leaves pointing away from the trunk and directing the rain where it 

 is most needed, whereas the soil near the trunk does not receive much 

 water. This feature admirably illustrates biological adaptation. 



