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geotropic in somewhat varying degrees; they lie indifferently 

 upon the surface of the ground; and thus arises the mode 

 of growth characteristic of Empetrum. Wherever circumstances 

 are favourable, its long, creeping shoot-systems will spread out 

 on all sides; the growth becomes decidedly espalier-like.^ But 

 unfavourable circumstances of locality, caused by the substratum 

 or by competing plant-growth; or disadvantageous circumstances 

 of light and wind; or possibly yet other factors, very often 

 interfere with the regular development of the espalier-like growth. 



Besides the long, creeping shoots, short, erect ones also 

 occur; sometimes on the more central portions of the single 

 individuals, where upward growth of the new shoots is com- 

 pulsory on account of circumstances pertaining to locality; 

 sometimes where, in many habitats, the external conditions 

 are such that the formation of short and erect shoots is in 

 excess of that of the long and creeping shoots. 



We may reasonably assume that the yearly addition to the 

 growth of the shoots is much less in an Arctic climate than 

 in southern regions. Naturally, in all places, it is the creeping 

 shoots which elongate the most; their internodes are longer and 

 their leaf-whorls more numerous than are those of the short, 

 erect shoots. But while the length-increment on Danish heaths 

 often amounts to about 10 cm., and sometimes even 14 or 

 15 cm., in Arctic regions the length of the long shoots is but 

 3—4 cm. at most, and often only 1 — 2 cm. Only in a single 

 specimen (from Disko) did I find the increase tu have been 

 either 5 or 7 cm. These few cases, in which the length-incre- 

 ment was greater, are doubtless due to special conditions of 

 the habitat — especially damp and shady soil— and also favourable 

 conditions regarding shelter. Unfortunately it is only rarely 

 that travellers give any information regarding this point; but 

 N. Hartz (in the Arctic Herbarium of the Botanical Garden) 



' Warming's term for prostrate, outspread growth. 



