312 CONIFEROUS FORMATIONS sect, xv 



be ascribed to the loose texture of the soil with its thick carpet of moss 

 and fallen needles. 



Plants that travel above ground are represented by Linnaea, Lyco- 

 podium clavatum, L. annotinum, Veronica officinalis, and others. But the 

 majority are strictly confined to their points of settlement, and possess 

 a multicipital primary root or a vertical root-stock bearing several stems. 



Grasses are very scanty in some forests, but numerous in others. 

 Cryptogamia are common. 



Most of the herbs show no xerophytic structure ; they are mesophytes 

 fitted to live in the shade and moist air of forest. But among the dwarf- 

 shrubs the evergreen ones are xerophytic. 



One peculiarity, in which northern coniferous forest contrasts with 

 dicotylous forest, is the abundance of dwarf -shrubs with fleshy fruits, 

 e. g. species of Vaccinium, Arctostaphylos Uva-ursi, Empetrum, and 

 Juniperus communis. This must probably be associated with the residence 

 within coniferous forest of birds that carry from place to place seeds and 

 fruits which they have swallowed or which adhere to their bodies ; in 

 this way Linnaea, species of Pyrola, and Goodyera have been introduced 

 into Danish pine-plantations only about a century old.^ 



Among the many kinds of coniferous forest those of Europe have been 

 the most completely investigated. Some of these are treated in the 

 succeeding paragraphs. 



Pine-forest (Pinetum). 



The Scots pine, Pinus sylvestris, can grow on very diverse soils, which 

 vary from dry warm sand, or rock with a thin layer of loose earth, to 

 moist, or even wet, soft bog-soil. It is an extremely accommodating tree, 

 capable of growing on very sterile soil, and in this respect resembles ling. 

 It is a light-demanding tree, whose inner branches therefore perish early, 

 so that the trunk gives way to a, bare bole ; the leaves remain attached 

 for only three or four years, and then only at the twig-ends and on the 

 crown. The ground is consequently often densely clothed with plants, 

 composed sometimes of one kind and at another time of another kind 

 of vegetation, 2 which varies according to the dryness and other 

 quahties of the soil, but is always in essence xerophytic and oecologically 

 closely allied to lichen-heath or dwarf-shrub heath. Sometimes Cladonia 

 rangiferina and other fruticose lichens, such as other species of Cladonia 

 and Cetraria islandica, thrive here better than on windy spots, and 

 extend over the ground as a whitish-grey carpet, in which are interspersed, 

 low, contorted hng-plants and others, including Linnaea, Arctostaphylos 

 Uva-ursi, species of Pyrola, Lycopodium annotinum, L. clavatum, Poten- 

 tilla sylvestris, Viola canina, and Maianthemum Bifohum. In other cases 

 mosses are commoner, or Juniperus communis, Vaccinium Myrtillus, 

 V. uliginosum, V. Vitis-idaea, Calluna, Populus tremula, and Empetrum, 

 are more frequent and taller ; in addition, Picea excelsa may occur as 

 a shrub forming underwood. A list of plants characterizing pine-forest 

 in North Germany has been compiled by Hock.^ There are northern 

 pine-forests whose soil has an extremely dry covering, which consists 

 of Arctostaphylos Uva-ursi, Juniperus, Calluna, Betula nana, Anten- 



' Warming, 1904. ^ Varieties of association, see p. 146. ' Hock, 1893. 



