392 PROTECTION AGAINST PLANTS. 



p. Parasites, such as dodder (Cuscuta), germinating on the 

 ground, but eventually attaching themselves to forest 

 plants. 



y. Parasites nourished partly by their own roots, and partly 

 by attaching themselves to useful plants. Broomrape 

 (Orobanche) on broom, furze, ivy, hemp, lucerne, etc. 

 Latliraca sqiiamaria, L., on the roots of trees, especially 

 hazel. 



xi. Epiphytes. Lichens do not remove sap from forest 

 plants, but live on water, air, and rotting bark, but when 

 attached to trees they are injurious by blocking the lenticels 

 and preventing necessary aeration of the internal tissues. 

 They harbour numerous insects, and increase the weight of 

 snow on the crowns of trees during winter. Trees with rough 

 bark, such as spruce, larch and pines, are most subject to 

 attacks of lichens, which increase in number with the age of 

 their hosts. The branches are more subject than the boles to 

 these attacks. 



Incrustating lichens, such as Imbricaria, Hatysma, and 

 Lecanora are worse than beard-like lichens, UsnJKij Ercrnia, 

 and Alectoria. Lichens do most damage in moist valleys and 

 in crowded woods. 



/' xii. Some weeds serve as hosts to injurious fungi, which 

 [may afterwards spread to forest trees or to agricultural crops. 

 Many parasitic fungi are most frequently found on weeds, 

 lor attack agricultural crops only after passing one stage 

 pf their existence on a weed. 



Thus, certain grasses e.g., Arrhcnathcrum and Arena 

 spread certain kinds of rusts on to cereal crops, such as 

 Tilletia caries, Tul., and Ustildgo carlo, Tul. Puccinia (jra~ 

 minis, Pers., on wheat comes from Aecidium Bcrberidis on the 

 barberry ; and oat-rust (P. coronata, Corda) from buckthorn. 

 Foresters should always look with suspicion on any fungus 

 appearing on wild plants. 



B. Special Forms of Damage done by Weeds. 



The amount of damage done to forests by particular weeds 

 depends on their wide dissemination and on the vigour mid 

 special nature of their growth. These are determined chiefly 



