ROOT-SYSTEMS OF PERENNIALS. 47 



Encelia is a very striking shrub, less than i meter high, with a close and 

 rounded contour. The ends of the rather sparingly branched shoots, which 

 are of a yellow-green color, bear large grayish leaves during the more moist 

 seasons, and drop all but the terminal small ones when the arid conditions set 

 in. Both leaves and flowers are formed whenever the water relations are 

 favorable. 



At the place where the specimen of Encelia was studied the malpais, 

 about 15 cm. in thickness, was underlaid by hard caliche of about the same 

 thickness, with a stratum of rotten caliche between, and this in turn was 

 resting on a layer of sandy malpais of undetermined thickness. 



The specimen selected for study was 90 cm. in height and was composed 

 of 12 shoots, all of which bore large leaves. The plant was mature and was 

 a very vigorous one. Its root-system was composed of a rather stout tap 

 root, running directly downward, and numerous laterals which arose com- 

 paratively far from the surface of the ground. The main root went straight 

 down through the malpais to the rotten caliche, where it narrowed abruptly 

 and ran through the rotten caliche to the hard caliche, through a crack in 

 which it made its way to the more deep-lying sandy caliche beneath. When 

 the latter was reached it turned abruptly and took a horizontal course for a 

 distance exceeding 50 cm. It was followed to a depth of 55 cm. beneath 

 the surface of the soil. 



The laterals of the first order, wdth no noteworthy exception, were given 

 off in the malpais stratum, that is, within 20 cm. of the surface, and were 

 placed between 15 and 30 cm. deep. There were about 5 main laterals; 

 they branched but little. The diameter, length, and position of the laterals 

 may be learned from measurements on one of the typical roots. The lateral 

 in question left the main root 15 cm. from the surface ; 15 cm. distant it was 

 6 mm. in diameter; at a distance of 60 cm. it was 2 mm. in diameter and 

 lay 24 cm. deep; i meter from the main root axis it was 24 cm. deep, and 

 at the tip, 1.5 meters distant, it lay 22 cm. beneath the surface. In addition 

 to the larger laterals there are about 6 shorter ones of the first order which 

 are wholly confined to the malpais. 



All of the laterals bore groups of filamentous roots, recalling those of 

 Aster tanacdifoUus, 5 cm. more or less in length, and about i cm. apart. 

 At the time the root-system of Encelia was studied, February 11, these 

 rootlets were no longer living, and the time of their origin is not known, but 

 is supposed to be much later than the formation of the mother laterals that 

 bear them. To judge from their appearance only,* one w^ould suppose 

 them to have been in part produced during the preceding year, probably 

 summer, and to constitute an important element in the absorbing system of 

 the plant. Further comment on this type of roots, which were observed on 

 several species, will be given below. 



*0n January 4, 1910, after rains had moistened the ground well, the roots of Encelia 

 were seen to bear young and growing rootlets of the kind described in the above 

 paragraph. 



