94 



THE ECOLOGICAL RELATIONS OF ROOTS. 



effective absorbing system, which ramifies widely and fills the soil from a 

 depth of from 4 to 36 inches. The whole root system is characteristic of the 

 half-gravel-sHde root habit. 



Besseya plantaginea. — This plant frequently grows in clusters of 3 or more, 

 the individuals of which are connected by short rhizomes about 5 mm. or less 

 in diameter and 2 or 3 inches long. The base of the plant and these rhizomes 

 are densely covered with fleshy roots about 2 mm. in diameter. As many as 

 30 to 40 of these roots occur on a single inch of the rhizome. Many of them 

 pursue a vertically downward course and end at a maximum depth of from 

 25 to 30 inches (fig. 39). Others run out rather parallel with the surface 

 of the soil and at a depth of 2 or more inches to a distance of over a foot, when 

 they turn abruptly downward, reaching a depth of 16 or 18 inches. Still others 



Fig. 39. — Besseya plantaginea, showing the widely spreading root system. 



fill in the angle between the horizontal and vertical roots, running off obfiquely 

 and then turning downward. Very few branches occur on the first 4 to 6 

 inches of the root. But beyond this point the roots (which are now a milH- 

 meter or less in diameter) branch freely, sending off laterals to a distance of 

 5 or 6 inches, the last 12 to 18 inches being so well branched and rebranched 

 as to form a fine absorbing network. Thus the soil within a radius of at least 

 a foot from the plant and at a depth of from 20 to 30 inches (except the sur- 

 face 2 inches) is rather completely filled with absorbing rootlets of this fleshy 

 perennial. As its root system shows, Besseya is an excellent illustration of a 



