6o ROOT HABITS OF DESERT PLANTS. 



together with vertical extension of two plants from West Wash, are shown 

 in fig. 6. The general character of the bases and the number of smaller laterals 

 are adequately shown in plate i6. Besides the larger branches of the main 

 laterals, which, as fig. 6 shows, were relatively few, there were groups of 

 filamentous roots occurring along their course as in Franseria and other 

 plants. Although not specially studied in Covillea, these rootlets were of 

 limited growth, ser^dng the plant for a short period only, as in the species 

 mentioned. 



The soil of the flood-plain by West Wash, where the other specimen of 

 Covillea studied was growing, was of adobe and sand to a depth exceeding 

 2.1 meters. The perennials of the habitat, both as regards kinds and num- 

 bers, were more numerous than on the bajada. Near the specimen of 

 Covillea from the flood-plain, whose roots were examined, were Acacia 

 greggii, Lyciuni andersonii, Parkinsonia torreyana, Prosopis velutina, and 

 other forms, mainly shrubs. 



The Covillea studied by West Wash was 1.65 meters high, or somewhat 

 larger than the bajada specimen examined, and, from the size and number 

 of the leaves and the character of the branching, it gave evidence of having 

 a better water supply than the bajada-grown plants. An examination of 

 the root-system of this plant showed that in certain ways it was very dif- 

 ferent from that of the plant from the bajada. The points of difference 

 appear well in comparing the vertical extension of the roots of the two 

 plants, as shown in the figures. The tap root was traced to its end at a 

 depth of 30 cm., although in another specimen growing near by the tap root 

 went down 1.7 meters, indicating that in the specimen under consideration 

 some calamity had brought about the untimely end of the main root. The 

 laterals were, in part, given ofif from the bases of the shoots and, after 

 leaving the main plant axis, had little uniformity in position. Some lay 

 20 to 45 cm. from the surface, others were still deeper. Such roots took 

 a more or less horizontal position. From these laterals branches were 

 given off, one of which went straight downward as far as 2.1 meters. 



Although the laterals of the first (?) order ran fairly horizontally as a 

 whole, they were not as long as the corresponding roots of the bajada- 

 grown plant; the radius included within the root-area did not exceed 2.2 

 meters, as opposed to nearly twice this figure in the other form studied. In 

 addition to the larger laterals just described, many smaller ones arose from 

 the bases of the shoots or from the bases of the larger laterals. As plate 16 

 shows, there were in the plant from the flood -plain man}^ more small adven- 

 titious roots than in the plant from the bajada. The laterals bore relatively 

 few branches. 



The root-system of the specimen of Covillea from the flood-plain may 

 be characterized, therefore, as having a deeply penetrating main root and 

 laterals which run in a fairly horizontal direction, although they may lie 

 as deep as 53 cm. and may give off branches that go straight downward. 



