402 PROTECTION AGAINST PLANTS. 



e. Birch. 



The two species of birch (Betula alba, L., and B. pubcsccm, 

 Ehrh.) ascend to 5,000 ft. The former is indifferent as to 

 soils, and the latter prefers boggy ground. They are sometimes 

 hurtful in coniferous forests, as their hard, whip-like branches 

 break off the tender spring-shoots of conifers. Owing to their 

 rapid growth when young they may be also prejudicial to 

 young oak plants, but may act as useful temporary nurses to 

 the latter against frost and drought. As birch has a number of 

 collmn-buds, it should be cut below the level of the soil. It 

 does not usually produce suckers. 



/. Other Lightdemanding Weeds. 



The best remedy for the remaining lightdemanding weeds 



is to effect natural regeneration of the wood, or to replant it, 



if clear-cut, as soon as possible. They are St. Jolm's-wort 



(Hypericum) ; balsam (Impatiens Noli-me -tang ere, L.), which 



grows in damp, fertile soil, in masses often a yard high and 



over large areas ; willowherb (Epilobiuui angustifolium, L.) on 



similar soil, the seed of which appears to remain latent for a 



long time, and is carried far and wide by the wind ; groundsel 



(Senecio), springing up in masses on sandy soils, the seed 



carried far by wind (these plants also act as hosts to parasitic 



fungi); hawkweed (Hieracium) ; Atropa Belladonna, L., on 



fertile damp soil in shady mountain forests of Europe and 



Asia (Himalayas), is very poisonous : foxglove (Digitalis) may 



grow in such masses that the hill-side appears red, both 



species, D. purpurea, L., and the yellow one, D. grandiflora, 



which is not indigenous in Britain, are poisonous; Vcrbascum, 



four species found on dry, stony ground ; nettles (Urtica urens, 



L.), an annual, and the perennial nettle, with strong rhizomes 



(U. dioica,"L.), are frequently troublesome in forest nurseries; 



wood-rush (Luzula) , tour species common in mountain forests. 



Grasses deserve a separate paragraph. The most common 



injurious kinds are: Species of bent-grass (Agrostis); Aim 



caespitosa, L., and A. flexuosa, L. ; Melica ciliata, L. ; sheep's 



fescue (Festuca ovina, L.), and other species of fescue ; couch- 



or twitch-grass (Agropyrum (Triticum) repens, Beauv.) ; lyme- 



grass (Elymns arenarim, L,) ; mat-grass (Nardus stricta, L.) ; 



