60 



THE ECOLOGICAL RELATIONS OF ROOTS. 



necting stems extend from 2 to 5 inches in depth and range in distance between 

 the plants from 1 to 15 inches or more. At the points from which the above- 

 ground stems take their origin, one or two roots were found which penetrated 

 the soil, usually vertically but occasionally obHquely downward, following a 

 tortuous course. These vertical roots at the outset may range from 0.5 to 

 2 mm. in diameter and gradually taper downward to their extremity, which is 

 more or less branched and hairlike. The maximum penetration found was 46 



Fig. 19. — Senecio aureus oblanceolatu^. 



inches. All parts of the root system, beginning about 2 inches below the soil 

 and extending to a depth of about 10 inches, are thickly supplied with small 

 laterals, usually about 0.3 mm. in diameter and from 0.5 to 3 inches in 

 length. These small laterals often come off in groups of 2 or 3. They are 

 themselves branched, ending in very minute capillary termini, thus affording 

 a very excellent system for surface absorption. The roots are white in color, 

 herbaceous, and for roots of this character fairly tough. When cut, small 

 amounts of latex exude. Six plants were examined (fig. 20). 



