CHAP, xiii.] Fungoid Diseases of Trees 299 



Infection appears invariably to take place at wound-surfaces 

 occasioned by causes of the most various nature (hail, removal 

 of standards, snow-pressure, injuries during clearing, weeding, 

 thinning, &c.). From such spots, frequently at the fork of 

 young branches, the mycelium penetrates into the woody tissue 

 and spreads quickly in a longitudinal direction up and down 

 the stem, when the wood infected becomes brown and dead. 

 As the mycelium develops, the canker seems to deepen into 

 the wood ; whilst the edges round the diseased part become 

 raised, and a hypertrophic condition ensues, which results in 

 spindle-shaped excrescences along the part attacked. The 

 branches or stems infected gradually become more and more 

 cankerous, until finally the pole or young tree is killed off. 



In order to prevent the spread of this disease, care should be 

 exercised in the felling and removal of standards, or of parent 

 trees above young seedling growth ; whilst all cankerous Beech 

 and Oak should be removed during the weedings and thinnings, 

 so far as possible without interrupting the leaf-canopy. 



Minor diseases are also occasioned by Nectria cinnabarina^ 

 a fungus very frequently occurring as small bright-red pustules 

 on the twigs and buds of Maple, Sycamore, Elm, Lime, and in 

 particular Horse Chestnut also by species of Poly poms ^ the 

 most important of which is P. sulphureus occurring on Oak, 

 Poplar, Tree Willows, Birch, and Larch. These species of 

 Polyporus, which also occasion red and white rot in timber, are 

 partly saprophytic, living only on dead wood, and partly true 

 parasites causing disease. In the latter case the mycelium 

 develops in the interior of the stem ; whilst the well-known 

 fructification of different shapes, often bracket-like, are situated 

 on the outside of the stem. The timely removal of trees thus 

 infected with fungus is advisable, not only in order to have 

 any use from the timber itself, but also for the purpose of pre- 

 venting the further spread of the disease through the formation 

 and scattering of spores. 



