Chap. I] THE FORMATIONS 



'73 



a warm vegetative season, a continuously moist subsoil, damp and calm 

 air especially in winter. 



Iiiniuiti-rid! for 7voodlaii(i is -.— whcihcr the moisture in the soil is sup- 

 plied by rain or by telluric water, whether the rain falls frequently or 

 rarely, or whether the rain falls during the period of activity or of rest. 

 To the optimum of the woodland climate corresponds the hygrophilous 

 tree, and to the lower grades of woodland climate, in descending order, 

 correspond the tropophilous tree, the xerophilous tree, and brushwood. 



Hostile to woodland in the higher latitudes is a climate with dry 

 winters, because, during the winter, trees cannot replace the water lost 

 n transpiration. 



ill. GRASSLAND CLIMATE. 



The demands that grassland makes on climate are quite difterent from 

 hose of woodland. As already stated, the grassy covering is the 

 :ontrolling feature of grassland. Formations of perennial herbs partially 

 )r entirely devoid of grasses cannot successfully contend against woodland 

 jrowth, and are found onl}- in deserts, as in the so-called Artemesia-steppes, 

 )ossibly in most cases mingled with brushwood. 



Herbaceous grasses are in the main inhabitants of temperate lands. 



n the tropics, we find luxuriant grassland, rich in grass, chiefly on the 



ligh plateaux that are periodically cool, for example in the interior of 



Brazil and in Central Africa, and a scanty growth of grass only where 



he temperature during the vegetative season constantly exceeds 30° C. 



.1 the daytime. It cannot be decided at present why high temperatures 



not suit most herbaceous grasses. During the season of rest, the 



ighest temperatures that occur naturally do not injure the parched carpet 



f grass. 



When compared with wood\- plants and many perennial herbs, the 



rasses composing the covering of grassland are shallozv-i-ooted plants, 



nd therefore suffer in prolonged drought during the vegetative season. 



: has been already mentioned what disastrous effects the dry vegetative 



:ason of the year 1893 had on grasses in contrast to woody plants 



nd deeply rooted perennial herbs, and VVoeikof has also cited similar 



bservations. A climate in which the dry and hot seasons are 



nchronous, like that of the countries bordering on the Mediterranean, 



consequently unfavourable to the growth of grass, and therefore also 



) grassland. Thus in August, i8(S6, near Lisbon I saw the grass and 



est herbaceous perennials quite dried up, while deeply rooted thistles 



ere blossoming gaily and trees displayed their foliage unimpaired. 



Moisture iu the subsoil lias little influenec on the covering of grass ; 



dy moisture iu the superficial soil is important to it. As the latter 



soon lost owing to evaporation and filtration, frequent, even if weak. 



