406 I'ROTECTIOX AOAINST PLANTS. 



//. Aspon {Popuhiri trenmhi, L.). 



Aspen is a tree which is disseminated throughout Europe, 

 except in the extreme south, up to 70° N. latitude, and 5,000 

 feet altitude ; it is often very hurtful to valuable forest plants 

 owing to its rapid growth and abundant production of suckers. 

 The roots of a felled aspen, which spread far from the stump, 

 close to the surface of the ground, remain dormant for years 

 after tlie parent tree has been removed ; they then send up 

 numerous suckers from adventitious buds after the wood in 

 which the aspen formerly grew has been cleared. The aspen 

 is not particular as regards soil, but can grow on cold, wet 

 soils, and is frequently found in frosty localities, as, for 

 instance, on the London clay in Epping Forest. 



The aspen is also a host for an injurious fungus, ISIclampsoya 

 Tremulac, TuL, which, in the forms M. Plnitorqua, Eostrup., 

 and M. Laricis, Harlig, attacks pines and larch, and will be 

 described further on (pp. 44-4, 469). 



Cutting down the suckers is of little avail, nor is extracting 

 the stumps and longer roots of felled trees, but girdling a 

 standing tree gradually dries it up and in about two years 

 prevents the formation of suckers. The tree may also be felled 

 about three feet above the ground, and the slump barked. 



h. Bilheny (Vaccinium Myrtillus, L.). 



This is a small shrub attaining 10 inches in height, and 

 growing throughout Europe up to 5,000 feet altitude, in masses, 

 on fresh, damp, and even somewhat sour soil. Its seeds remain 

 for two seasons in the ground before germinating. It may also 

 be found on dry sandy soils, but not on calcareous ones. It 

 prefers a slight shade, especially of pines. When it appears in 

 masses it denotes insufficiency of stock and deterioration of 

 the soil, and the surface-soil becomes choked with its roots. Its 

 berries are valuable for making alcohol and preserves. 



The cowberry {Vaccinium Vitis-Idaea, L.) is an evergreen 

 plant attaining 8 inches in height, and growing on loose, 

 damp, sandy soils in high, cool places ; it is gregarious, and has 

 a distribution similar to that of the bilberry, growing, however, 

 in moibter soil than the latter. A dense growth of either of 

 these species hinders natural regeneration and increases the 



