184 NORTHERN ZONE OF COLD WINTERS 
Those flowers which like Vaccinium, Erica, Calluna, &c., 
or Alchemilla, Saxifraga, Potentilla, &c., are adapted to 
one or other of these groups, form the chief features of the 
entomophilous flora of these regions. Anemophilous flowers 
(e.g. Thalictrum, Cyperaceae, Juncaceae, Gramineae) are very 
abundant. Vegetative reproduction is common (especially 
interesting cases are Polygonum viviparum , Saxifraga 
cernua , &c.) and in general the floral features and 
mechanisms resemble those of the arctic regions. In the 
Alps it is different. At high levels butterflies and moths 
abound, and the flowers adapted to them figure largely in 
the flora, e.g. Gentiana, Viola, Silene, Dianthus, Daphne, 
Primula, &c. Insect visitors are present in sufficient 
numbers to enable most flowers to do without much self- 
fertilisation or vegetative reproduction. They have appa- 
rently determined the evolution of the endemic species into 
butterfly-flowers, &c., for there are many cases where the 
alpine species of a genus belongs to class F, the lowland to 
classes with shorter tubes, e.g. H. The flowers of alpine 
plants show, in general, brighter colours than those of low 
levels ; this is apparently a direct effect of the brighter light. 
II. Northern zone of cold winters \ This extends 
from the northern limit of trees to the latitude in which 
evergreen branched trees and shrubs begin to predominate, 
and in which the country is parched in summer. It reaches 
in Europe to the south of France and to Greece, and in 
Asia to about 50° N. ; in North America it includes most of 
Canada, the western United States as far south as Utah, 
and the New England States. Corresponding areas occur 
in the various mountain-ranges. The period of vegetation 
lasts during 3 to 7 months, with its maximum in July; the 
1 Schimper, Warming, etc., op. cit. ; Flahault, Essai Pune carte 
botanique et forestiere de la France , Ann. de Geog., 1897; Graebner, 
Studien iiber die norddeutsche Heide , Engl. Jahrb. xx, 1895 (and cf. 
recent volumes of this journal) ; Sernander, Den Skandinaviska 
vegetationens spridningsbiologi, Upsala, 1901 (cf. Bot. Centr. 88, 380) ; 
Engler, Die pflanzengeographische Gliederung Nordatfierikas , Notizbl. 
k. Bot. Gtns., Berlin, 1902 ; Pound and Clement, Vegetative Regions of 
the Prairie Province, Bot. Gaz. xxv, 1898, p. 381, and many papers in 
same journal in recent years by these authors, Cowles, Livingston, etc.; 
Macmillan, Minnesota Plant Life y St Paul, 1899; and cf. above, 
Halophytes, Alpine Plants, etc. 
