120 Botany 



shoot modifications induced by environmental agencies lie within well-defined limits. 

 This range of variation being thus comparatively narrow, a high degree of special- 

 ization in habitat results in desert soils. The root-systems of the rapidly growing 

 summer annuals of the desert are different from those of winter annuals in show- 

 ing a fuller development of all components, but neither type penetrates the soil to a 

 greater depth than 20 cm. (8 inches). Perennials have three types of roots namely, 

 the generalized type, with the tap-root and the laterals both well developed, and the 

 specialized forms, of which one type has a prominent tap-root and the other promi- 

 nent laterals. Covillea tridentata and Prosopis velutina are representatives of 

 plants with generalized roots, while Kceberlina spinosa and a few other plants have 

 specialized roots of the second type. 



No. 178. CANNON, W. A. Botanical Features of the Algerian Sahara. Octavo, 



vi+81 pages, 37 plates. Published 1913. Price $2.50. 



This report gives the more important observations made by the author in the au- 

 tumn of 1910 and early spring of 1911 in southern Algeria and interprets the main 

 characters of the flora in the light of results previously attained at the Desert Labo- 

 ratory at Tucson, Arizona. The territory visited was from Laghouat, just south of 

 the Saharan Atlas Mountains, across the regions of the Daya and the Chebka, to 

 Ghardaia, the chief city of the M'Zabites. From Ghardaia the Gantra was crossed 

 to Ouaragla and thence the route followed was by Touggourt and the Oued Rirh 

 to Biskra. Special attention is given to the root habits of the shrubs and semi- 

 shrubs which are related so far as possible to the environment. A portion of this 

 region visited has been little seen by botanists and the descriptions of plant habits 

 and their habitats are thus far new. The study is illustrated by many detailed 

 and general pictures of plants and of their environment. 



CANNON, W. A. The Topography of the Chlorophyll' 



No. 98. 



Apparatus in Desert Plants. Octavo, 42 pages, 15 

 text figures, 5 plates. 



KNOX, ALICE A. fnduction, Development, and Herita- 

 bility of Fascialions. Octavo, 20 pages, 1 text figure, 

 5 plates. 



Published 

 1908. 



Price 

 $0.75. 



(a) The results of a developmental study of the chlorophyll apparatus of a 

 number of species characteristic of southwestern deserts. Essentially different 

 mechanical arrangements and functional specializations are found in species with 

 reduced leaves and those with extensive, deciduous, laminar formations. The con- 

 ditions governing the thickness and duration of chlorophyllaceous layers in organs 

 subject to secondary thickening are analyzed and some interesting arrangements 

 in succulents and green stems described. 



(fc) A morphological study based upon living material, showing the principal 

 anatomical features in a number of types of fasciations, together with the results of 

 some extensive experimental observations upon their induction. The heritability of 

 the structures in question was tested by pedigree cultures through several generations. 



No. 113. SPALDING, V. M. Distribution and Movements of Desert Plants. Oc- 

 tavo, v-f-144 pages, 31 plates, 3 figures. Published 1909. Price $2.00. 



This paper embodies the results of a study of the factors governing distribution 

 over an area of 4 square miles, including a varied topography, together with col- 

 lateral data from a much larger area. The author has made an exhaustive experi- 

 mental analysis of the relations of the plants of the desert to habitat conditions. 



The species encountered may be divided into four main groups, according to 

 their habits in the river, in the flood-plain, on the slopes or bajadas, and on the 

 hills or cliffs. Physical properties of the soil, such as soil-moisture and aspect or 

 exposure, are found to be the paramount factors in the determination of local dis- 

 tribution. A large number of the species exhibit a wide range of adjustment and 

 accommodation, particularly with respect to water-supply and temperature. The 

 competitive feature among plants is emphasized as a result of these studies. 



