CLIMATIC FACTORS 119 



Lakari (1920) found that snow injury of spruces in Finnish forests 

 led to reduction of annual growth and decreased crops of cones and 

 seeds. 



Further harm is due to the favoring of certain parasites by the snow- 

 cover. The parasitic fungus Her'potrichia nigra (Sphaeriaceae) envel- 

 ops the twigs of Pinus montana and Juniperus nana in snowy hollows 

 with a dark brown, slimy mycelium killing whole plantations, while the 

 same species hard by, but covered for a shorter period with snow, suffer 

 little or no injury. 



In the regions of snow injury in Finland a number of fungus para- 

 sites are often very destructive (especially species of Fomes, Fomitopsis, 

 and Trametes pini). Lakari (1920) studied snow injury in forests 

 minutely and reviewed the literature. 



Snow-favored and Snow-injured Species. — In snowy regions two 

 extreme groups of plants may be distinguished: those species favored 

 by snow (chionophilous species), which occur only where they are 

 covered late in the season by snow; and those injured by the snow 

 cover and seemingly avoiding snow (chionophobous species), which are 

 not found where the snow lies long upon the ground. A few species 

 are more or less indifferent to the duration of snow cover but occur 

 both on permanently snowless areas and in places with prolonged snow 

 cover, e.g., Poa alpina, Agrostis rupestris, and Carex m'gra in the Alps. 

 Chionophily and chionophoby depend primarily upon the greater or 

 lesser resistance of the species to cold and drought. But chionophilous 

 plants must be able to continue their life processes in almost total 

 darkness under the snow and bloom and fruit within a few weeks after 

 the melting of the cover. 



The injurious effect of artificial removal of snow cover from 

 vegetation accustomed to being covered for several months was studied 

 by Grisch (1907) in a Trisetum flavescens meadow at 1,240 m. The 

 uncovered area showed not only a rapid change in the proportionality 

 of the species but also a great reduction in the amount of vegetation 

 produced. The number of seedlings in May was 17 per square foot on 

 the snowless area, against 104 on the snow-covered area. 



Since the seeds of many alpine plants germinate in late autumn and 

 winter, and many species overwinter with green shoots, without any 

 autonomous winter rest, or are very easily stimulated to growth (cf. 

 Braun-Blanquet, 1913, pp. 45-52; Riibel, 1926), it is especially in high 

 mountains that the importance of snow cover is most obvious as protec- 

 tion from cold and drought. 



Woeikoff (1889, p. 14) in Petrograd on Mar, 10, 1888, took the 

 following temperatures, showing how cold decreases with depth of 



