34 root habits of desert plants. 



Erodium Cicutarium. 

 Erodiiim ciciitan'iiiu, which is an introduced species, has already a wider 

 distribution in this vicinity than most native plants and promises to become 

 one of the most successful of the winter annuals (Spalding, Distribution and 

 Movements of Desert Plants, Carnegie Institution of Washington, Publi- 

 cation 113, 1909, p. 27). Although its root-system was not studied closely, 

 there are some points of interest that may be referred to. The dominant 

 features of the root-system are the prominent tap root and the poor devel- 

 opment of the laterals. How deep the tap root penetrated was not accu- 

 rately learned, but its length is believed to equal that attained b}'- the roots 

 of most perennials occupying the same habitats. The laterals were most 

 numerous about 4 cm. beneath the surface of the soil, and in the specimens 

 examined averaged only 1.7 cm. in length. 



Festuca Octoflora and Hordeum Murinum. 



Two biologic types of grasses, annuals and perennials, occur on Tumamoc, 

 each of which appears to have its characteristic distribution. The annual 

 grasses, both those of summer and those of winter, are generally distributed, 

 but the perennial forms occur where the water relations are especially 

 favorable. Of the grasses only two winter-growing ones were examined. 

 The type of the root-system of the grasses is well known so that there is 

 no need of presenting a description of it in detail ; but it will be instructive 

 to compare the extent of the root-system of the grasses with that of the other 

 annuals w^hich appear at the same season. 



In the mature plants the roots are entirely of secondary origin, and 

 there is no main root to dominate the system. The length of the roots 

 is variable but considerable. In a plant with a shoot 17 cm. long there 

 were 3 large roots, each about 5 cm. in length, with numerous branches 2 

 cm. in length, more or less. Another plant (both were of the genus Festuca) 

 19cm. high had 4 roots over 12 cm. long. The laterals borne on these roots 

 were filamentous and varied greatly in length (some being 10 cm. or more), 

 and bore in turn long and short filamentous branches (plate 6) . 



The root system of Hordeum was similar in character and approached in 

 extent that of Festuca. A plant with a shoot 22 cm. in length had 4 large 

 roots, all of which were over 14 cm. long; and another specimen with a shoot 

 30 cm. long had 7 large roots, of which the longest was over 17 cm. All 

 bore numerous filamentous branches. The depth of penetration of the 

 laterals w^as not learned. It may be safely assumed, however, from other 

 observations as well as from those just presented, that the roots reach at 

 least 15 cm.; perhaps still deeper in the largest specimens. 



GiLIA BiGELOWII. 



Gilia bigclowii, one of the smallest winter annuals, is generally distributed 

 on Tumamoc Hill. The roots of Gilia are admirably adapted to enable the 

 plant to reach relatively deep, while at the same time it takes advantage 



