296 BOTANICAL GAZETTE [October 



higher slopes. These ruderals are characteristically confined to 

 marginal invasion, though they are frequently found wherever the 

 open association makes possible their estabhshment. Onagra, how- 

 ever, is able to establish itself in the closed formation, as is Potentilla 

 monspeliensis. Hordeum especially makes advance where some 

 artificial agency has destroyed the equihbrium in rich moist stations; 

 frequently in such cases it assumes even facial rank. 



The 90 prairie elements proper have a most interesting taxonomic 

 distribution. The composites with 29 species (32.2 per cent.) form 

 the dominating family, comprising nearly a third of the total forms. 

 The Gramineae number 15 species (16.6 per cent.), and though not 

 leading in species they rank first in number of individuals. The 

 third important family is the Leguminosae with 11 species (12.2 

 per cent.). Thus these three famihes provide 61 per cent, of the 

 prairie elements and perhaps over 90 per cent, of the individuals. 

 The remaining 35 species (39 per cent.) are conspicuous on account 

 of their diverse affinities, belonging as they do to 22 different families, 

 14 of which have only a single representative in the formation. The 

 famihes are as follows: Borraginaceae (4), Ranunculaceae (3), 

 Cyperaceae (3), Onagraceae (3), Scrophulariaceae (2), Linaceae (2), 

 Rosaceae (2), OxaHdaceae (2); and the following with one species 

 each: Nyctaginaceae, Cruciferae, UmbeUiferae, Iridaceae, Violaceae, 

 Euphorbiaceae, Caprifoliaceae, Solanaceae, Labiatae, Plantagina- 

 ceae, Gentianaceae, Verbenaceae, and Polygalaceae. 



The life conditions of the formation are by no means equable, 

 and in this relation it is significant to record that only 11 per cent, 

 of the species are annual, the majority of which produce abundant 

 seeds and are provided with efficient means of distribution and occur 

 mainly in the xerophytic open associations. Of the remaining 89 

 per cent, which are perennials, 96.2 per cent, are geophytic; Rosa, 

 Symphoricarpus, and Amorpha alone are woody. 



In a region characterized by strong prevailing winds it is to be 

 noted that a high percentage of the species is wind-distributed. 

 An analysis of this point shows that about 90 per cent, are so dissem- 

 inated, some 55 per cent, showing especial facihties to this end. 

 The great range of specific forms and their marked frequency in 

 the formation finds an explanation in this permobility of repro- 



