82 



THE ECOLOGICAL RELATIONS OF ROOTS. 



eter, which reaches depths varying from 20 to 30 inches (fig. 31). Except for 

 the first 3 to 5 inches, where the plant tops have shpped down the gravel 

 sUde, the root pursues a rather vertically downward course, the tip being only a 

 few inches horizontally away from the base of the plant, in spite of the back- 

 ward and forward meanderings of the root through bends of 3 or 4 inches in 

 diameter. The tap is often flattened and kinked where it forces its way 

 through the crevices of the semi-decomposed rock. The number of larger 

 branches is few, usually not exceeding 2 or 3. One plant gave off only one 

 large branch, about 2 man. in diameter, at a depth of 3 inches. As is charac- 

 teristic of numerous other plants examined, this lateral branched freely and 

 ran off in a direction nearly parallel with the surface for about 15 to 20 

 inches, ending in a network of well-branched rootlets. On another plant a 

 lateral ran off more than 36 inches from the base of the stem, branching again 

 and again. Other smaller branches arise from the tap in great abundance. 

 These are only a few centimeters long, but well-branched and densely covered 

 with root hairs. The older cortex is black and of a papery texture, peeling off 

 readily. 



Paronychia jamesii. — This small, cespitose perennial forms a consocies of 

 the community. It has a tap-root about 5 mm. in diameter. Like all other 

 plants on the gravel-shde, the top has been pushed down the slope several 



Fig. 32. — Paronychia jamesii. 



inches. The tap breaks up into several larger laterals, usually 3 to 5, and a 

 great number of smaller ones. Some of the laterals run off in a horizontal 

 direction to a distance of 30 inches or more, at about 2 to 4 inches in depth, 

 branching repeatedly, as shown in figures 32 and 33, and being abimdantly 



