70 



RoiiT MAllITS i>K HKSICkT PLANTS. 



respondinfj roots of all oiIrt opuntias seen, branched repeatedly through- 

 out their course, in places forming a network closely covering the ground. 

 The laterals extended for about t, meters and lay so near the surface of 

 the ground thai the tips could be lifted out with a walking stick, and thev 

 could be torn out of the ground their entire length. More exactly stated, 

 the roots lie from 2 cm., and even less, to 8 cm. beneath the surface. 



I'iG. 1 1. — Horizontal extension of root-system of Opuntta arbusciila. Black dots indicate position 

 of CLnilU-a Irideittalii which had invaded the root-area of the cactus. 



As compared with the roots of other opuntias, those of aibuscula are 

 large (plate 18). This will be appreciated from the following measure- 

 ments. A meter from its base one of the larger roots had a diameter of 

 2.5 cm., 2 meters distant it was 2 cm., 3 meters distant it was 1.5 cm. The 

 tips of these roots, excluding the most recent growth, were not less than 

 I cm. in diameter. From the size and tuber-like appearance of the roots it 

 was concluded that they function as water-storing organs. This conclusion 

 was strengthened by the obser^-ation that inside of 48 hours after the roots 

 of this plant ^vere removed from the soil they were rapidly losing their 

 plump aspect and had begun to slnivel strikingly. A noteworthy pecuU- 

 arity of the larger roots was their frequent abrupt ending through the death 

 of the more distal portion. 



The lleshv roots of aibi<sciila. in addition to functioning as water-storing 

 organs, a rare root-character among mature opuntias, further ser\'^e as prop- 

 agating organs, and to this function the occurrence of the species in masses 

 is due. The procedure, in brief, is this. One or more shoots may arise 

 from a single lateral while the latter retains its connection with the jiarent. 



