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 establishment. Onagra, how- 
ever, is able to establish itself in the closed formation, as is Pofentilla 
mons peliensis. Hordeum especially makes advance where some 
artificial agency has destroyed the equilibrium 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 families provide 61 per cent. of the 
prairie elements and perhaps over go 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 
families are as follows: Borraginaceae (4), Ranunculaceae (3); 
Cyperaceae (3), Onagraceae (3), Scrophulariaceae (2), Linaceae (2), 
Rosaceae (2), Oxalidaceae (2); and the following with one specie 
each: Nyctaginaceae, Cruciferae, Umbelliferae, 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 ? ¥ 
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; —_ 
Symphoricarpus, and Amorpha alone are woody. as 
In a region characterized by strong prevailing winds 1t !s to : 
noted that a high percentage of the species is wind-distribu : 
An analysis of this point shows that about go per cent. are so een 
inated, some 55 per cent. showing especial facilities to this €” 
The great range of specific forms and their marked frequency si 
the formation finds an explanation in this permobility eee 
