446 A TREATISE ON METAMORPHISM. 



base and 1 meter below the surface. Apple trees have been known to 

 send roots 14 meters from their bases. In one case a long-leaf pine in 

 Alabama was found to have extended its roots to a depth of 9 meters, and 

 at this depth the taproot had a diameter of 20 cm. It is to be presumed 

 that the gigantic trees of western America and the Tropics extend their 

 roots even deeper. 



In this connection it is to be remembered that various kinds of plants 

 work together. For instance, in warm humid regions trees are very 

 numerous. Between the trees are other plants of many kinds. Thus we 

 are lead to the conclusion that wherever the vegetation is luxuriant above 

 the surface of the earth there is almost an equally luxuriant growth below 

 the surface. Wherever there is a cornfield, a wheat field, or a clover field, 

 corresponding with the plexus of stems and leaves above the ground there 

 is another plexus of roots below the ground almost equaling that above the 

 ground in extent, and pervading it throughout with roots varying in size 

 from the most minute hair-like rootlets to the taproots of the plants. 

 Wherever there is a forest the great bulk of trunks and limbs and twigs 

 above ground is almost paralleled below ground by the tangle of roots, 

 grading from the mighty taproot to the minute rootlets. 



As the roots grow they thrust the soil or the rock aside. As they 

 decay, openings are left which are taken advantage of by downward- 

 moving water. Gravity tends to pull the soil or rock together again, and 

 thus finally close the larger openings. But in the meantime others are 

 made by the growing vegetation. Thus where there is abundant plant 

 life the rock material to the depth to which the roots extend is being 

 constantly moved about. 



Therefore, if we would understand the entire work of the plants, 

 wherever we see the foliage of field or forest above the ground we must in 

 our mind's eye see a nearly equal volume of roots below the surface of the 

 earth, prying the soil apart, splitting the rocks, and, as explained below, 

 acting upon them chemically. 



Finally, when large plants, especially trees, fall a further mechanical 

 effect follows. It has already been seen that trees may extend large roots 

 into the ground to a depth of a number of meters, both laterally and 

 vertically. When a tree is overthrown by the wind, or in some other way, 

 a large mass of the soil, subsoil, contained bowlders, and even the solid 



