402 I'ROTECTION AGAINST PLANTS. 



e. Birch. 

 The two species of birch {Betula alha, L., and B. piihcscens, 

 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 

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

 does not usually produce suckers. 



/. Other Lif/hfdema?i(/iiiff 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. John's- wort 

 {Ilij^ycricum) ; balsam {ImjKiticns NoU-me-tangere, L.), which 

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

 over large areas ; willowherb {Epilobium cwf/nstifoUuin, 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 

 {Seuecio), springing up in masses on sandy soils, the seed 

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

 fungi); hawkweed (Ilieracium) ; Atrojm Belladonna, L., on 

 fertile damp soil in shady mountain forests of Europe and 

 Asia (Himalayas), is very poisonous : foxglove {DuiitaUs) may 

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

 species, I). pHrpurea, L., and the yellow one, D. f/randi flora, 

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

 four species found on dry, stony ground ; nettles {Urtica nrens, 

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

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

 wood-rush {TAizida),iouY species common in mountain forests. 



Grasses deserve a separate paragraph. The most common 

 injurious kinds are:— Species of bent-grass {Agrostis); Aira 

 caesjntosa, L., and A.flexuosa, L. ; Mclica cdiata, L. ; sheep's 

 fescue {Fesiuca ovina, L.), and other species of fescue ; couch- 

 or twitch-grass (Ar/rojii/rum {Triticum) repens, Beauv.) ; lyme- 

 grass {Khimus arrnarius, L.) ; mat-grass {Nardus siricta, L.); 



