LIST OF FOREST WEEDS. 419 



growing on Euphrasia and Tussilago also produce pine-needle 

 blister. 



The aspen (Populus Tremula, L.) has its leaves infected with 

 a fungus, Melampsora pinitorqua, Eostrup., so that its foliage 

 may appear quite golden-yellow in August, and then rapidly 

 fall. The sporocarps of this fungus on aspen leaves eventu- 

 ally turn dark brown, hibernating on the fallen aspen leaves, 

 and in the spring, the spores infect Scots pine and larch 

 with the fungi. The alternate forms (pp. 444, 470) on pine 

 and larch will be described in the next chapter. 



Vaccinium Vitis-Idaea, L., acts as host to Melampsora 

 (C alyptospora] Goeppertiana, Kiihn, which, growing on the 

 stem of this plant, develops spores infecting the needles of 

 silver-fir with Aecidium columnare, Alb. (p. 462). 



Species of juniper form the alternate hosts of several 

 species of Gymnosporangium, a rust-fungus attacking several 

 pomaceous species : 



Gymnosporangium davariaeforme, Jacq., infects the common 

 juniper, and its spores subsequently attack pears, hawthorns, 

 or whitebeams (Pyrus Aria, Ehrh.) 



G. Sabinae, Winter, on the common juniper and on the 

 savin (Juniperus Sabina, L.), also occurs on pear trees. 



(3. confusum, Plowr., spreads from junipers on to pears, 

 medlars, quinces and hawthorn. 



G. juniperinum, Winter, occurs on rowan (Pyms Aucuparia, 

 Gaertn.), and perhaps on apple leaves. 



Species of starwort (Stellaria) and Cerastium are the hosts 

 of a fungus causing silver-fir canker and witches-broom 

 (p. 448). 



The forester should always look with suspicion on weeds 

 or shrubs in his forests that may be infested with fungi, and 

 if the injuriousness of these fungi to agricultural' crops or 

 forest or fruit-trees is proved, he should if possible eradicate 

 the wild plants on which they first appear. 



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