ROOT HABITS OF DESERT PLANTS. 



Daucus Pusillus. 



Daticus l?usillus, one of the most generallydistributed of the winter annu- 

 als, is abundant on both Tumamoc Hill and the upper portion of the bajada 

 north of the Hill. Its root-system can be characterized as being extensive 

 rather than intensive. The main root dominates the root-system, although 

 it is never fleshy, or even very coarse, and the laterals are relatively few 

 and branch but little. 



Young as well as mature plants were studied. The tap root of a plant 

 whose shoot was i8 cm. long and which was in flower was over 15 cm. long. 

 Just beneath the surface of the ground, where the tap root was sHghtly 

 over I mm. in diameter, several fine roots, but not filamentous, were given 

 off' about 3 cm. from the surface of the ground, and 3 to 4 cm. deeper a prom- 

 inent lateral, 7 cm. in length, had its origin. Roots of the second order were 

 few in luimber. As plate 5 shows, there is no great difTerence in diameter 

 between the main root and the laterals, or between the laterals of the first 

 and the second order. 



The leading feature which marks the mature plant is characteristic of the 

 young plant as well. Thus a seedling with seed leaves and only one leaf of 

 the adult type had an unbranchcd tap root over 5 cm. long, while another 

 of about the same age had a tap root over 6 cm. in length, which every 3 to 

 12 mm. bore laterals about 2 mm. long. This type of root-system was 

 seen also in a somewhat older plant. It may be concluded, therefore, that 

 Daucus not only penetrates the ground deeply (how deep was not deter- 

 mined), but also quickly, and is thus admirably adapted to endure after 

 more shallow-rooted annuals have perished . 



Eritrichium Pterocaryum and Harpagonei.la Palmeri. 



Eriinc/! »()» and H(7;7'a(/oKc//a, two boraginaceous winter annuals, although 

 relatively small, usually considerably under 15 cm. in height, and thus 

 inconspicuous as to individuals, occur in such great numbers that they 

 constitute an important element in the plant covering of their favorite 

 habitats. These are common on Tumamoc Hill as well as on the upper 

 portion of the bajada to the north of the Hill. Plants of difi"erent ages 

 and from diff'erent localities were examined. A mature specimen of Eri- 

 trichimn, with the shoot 13 cm. long, had a filamentous tap root which 

 penetrated over 8 cm. The laterals were borne in the region between 3 and 

 6 cm. from the surface of the ground, and were 4.5 cm., and less, in length. 



The root-system of Harpagonellawas somewhat better developed ; plants 

 from dry and moist situations were stvidied. Those from the drier locations 

 had unbranched shoots 7, g, and 10 cm. in length. The roots of the smallest 

 plant penetrated over 1 1 cm. The laterals were given oft" from the main 

 root from i to 4 cm. beneath the surface of the ground. The specimen of 

 Harpagondla from the more moist soil, with a shoot 19 cm. long, had a tap 

 root which was followed over 15 cm. The laterals, like those of the plant 

 from the drier situation, were unbranched. 



