EFFECTS OF GROWING CELLS ON ENVIRONMENT. 



615 



of stone are composed for the most part of crystalline schist, especially of gneiss, in 

 which mica is arranged in almost parallel streaks. On one of these blocks (repre- 

 sented in fig. 130), at a height of 2 metres, a larch has long ago established itself 

 and rooted firmly, so that the strongest of its roots grow downwards in a cleft 

 parallel to the direction of the mica streaks. By the thickening of this root the 

 crevice became widened; half of the upper block was separated from the lower and 

 was raised about 30 cms. It is estimated that the weight of this raised portion 

 amounts to 1400 kg., and the root which was able to raise this burden exhibits in 



Fig. 130.— Elevation of a Block of Stone in consequence of the growth in thiclcness of a Larch Root. 



its thickest part a diameter of only 30 cm. Moreover, the burden overcome by this 

 larch root is small in comparison with that raised by the roots of old trees. The 

 large superficial roots which creep over the ground of the forest like gigantic snakes 

 were not always situated in this position. As long as the trees were young their 

 roots extended under the ground. Only with increasing thickness did these roots, 

 pressing against the firmly compacted earth lying beneath them, become visible above 

 ground, since they burst through the layer of earth situated above them. But with 

 this must also be connected the elevation of the whole trunk with its boughs, which 

 all bear upon the roots, and often weigh several thousand kilogrammes. 



It is a matter of course that growing stem-structures also exercise a considerable 

 pressure on their environment. Those underground stems which are called runners 

 do not in this respect difi'er materially from roots, and are similarly able to shift 



