CHAP. LXXIV GRASS-STEPPE 283 



hills, 1 and rather on coarse-grained sand or gravel, into which water 

 can more easily enter, than on heavy loam soil. 2 



Steppe has a continental climate. The summer is extremely hot and 

 dry ; the winter very severe and long, with violent snow-storms. Spring 

 commences late. The vegetative season lasts for only two or three 

 months (from April to June in Europe) ; plants shoot rapidly forth from 

 the soil, and, just like desert in the moist season, the steppe is fresh- 

 green and shows a wealth of blossom. When summer arrives the vegeta- 

 tion assumes a greyish-green, faded tone, while the soil cracks and becomes 

 dust. The moisture in autumn may again call forth verdure on the 

 steppe ; and apart from certain species of Artemisia and other plants, 

 autumn is specially the season of annual Chenopodiaceae and similar 

 halophilous herbs. The snow during winter is an important source of 

 water-supply to the vegetation. 



The appearance presented by steppe also depends upon the relief 

 of the surface, which is such as to allow the wind to play freely and 

 violently over vast plains and thus to increase evaporation. 



Growth-forms. The vegetation consists of a varied admixture of 

 annual and perennial herbs, grasses, and undershrubs. It is easy to see 

 that the external conditions must call into being xerophytic vegetation. 



The perennial herbs ensure their lives by subterranean parts that are 

 protected from complete desiccation under the soil. 



Some of the plants are spring-plants with bulbs or tubers ; for instance, 

 in the Orenburg District there is a gay show of Liliaceae (including 

 Fritillaria, Allium, Scilla, Gagea, and Tulipa), Iris, Corydalis, and Adonis 

 vernalis. 



Many perennial herbs, which develop later, have deeper tap-roots, 

 and often (particularly toward Asia) grey-haired shoots ; these include 

 Labiatae, Cruciferae, species of Artemisia, Caryophyllaceae, Malvaceae, 

 Papilionaceae, and many grasses which form the main mass of vegeta- 

 tion and impart its general tint. The last-named are perennial tufted 

 grasses ; the tallest tufts consist of species of Stipa ; the leaves are narrow, 

 stiff, and often setaceous, and often persist for months, though in a faded 

 state. 



Many annual, short-lived species occur here and there ; in this respect 

 steppe contrasts not only with subglacial tracts, but also with the meso- 

 phytic meadows and fields of north-temperate Europe. 



Undershrubs occur, but shrubs and trees are wanting. 



Investigation will probably show that some seeds are dispersed by 

 wind, others by animals, as is the case in other types of vegetation. 



The luxuriance and richness of this steppe vary widely with the 

 geographical situation, and depend mainly upon the nature of the soil. 

 On the most fertile South-Russian steppe, where soil is the ' black earth ' 

 already mentioned, Festuca ovina and Koeleria cristata dominate, together 

 with Medicago falcata, Thymus Serpyllum, and others. On less fertile 

 steppe thyrsa-grass (Stipa pennata and S. capillata) is more abundant, 

 while perennial herbs are less represented. The most sterile steppe is 

 occupied almost solely by tall tufts of xerophytic thyrsa-grasses, and 

 particularly by those of Stipa pennata. The degree to which the soil is 



1 Middendorf, 1867; Tanfiljew, 1905. * Kostytscheff, 1890. 



