288 Studies in Forestry [CHAP. xin. 



pustules on the whitish streaks along the under surface. In 

 consequence of infection the needles change colour, turn 

 brown, and drop off from the twig, to which they remain 

 suspended by the mycelium. The pustules turn brown after 

 the drying-up of the needles ; and about November small, 

 round, blackish-brown, hairy Peritheda are formed containing 

 the dirty grey spores, which germinate easily on Silver Fir 

 foliage and thus spread infection. But the mycelium hibernates 

 on the sprays and needles, and extends to the new shoots 

 developing in spring, whose foliage it attacks as well as the 

 needles that may hitherto have escaped on the old sprays. In 

 addition to scattering abroad myriads of spores, this fungus 

 never relaxes its attacks or quits the foothold it may once have 

 attained on any young tree, until the latter has been killed. This 

 disease occurs most frequently in twenty to forty-year-old crops 

 of Silver Fir, especially on the lower foliage and on individuals 

 of most forward development ; but it is also to be found on 

 Spruce. The best remedial and protective measures consist in 

 the cutting out of infected twigs, and in careful tending so 

 as to maintain a good canopy and keep the woods as free as 

 possible from tangled growth. 



B. On Broad-leaved Trees : 



i. Phytophthora omnivora, de Bary, the Beech-seedling 

 Fungus. 



The effects of this disease were first noticed in the cotyle- 

 donous leaves of Beech-seedlings. They manifest themselves 

 in the withering of either the slender stalk or the rootlet, and 

 in black spots at the base of the cotyledons or on the pri- 

 mordial leaves when these appear. Within about a week of 

 the first symptons of disease the whole seedling exhibits its 

 effects, especially when May and June are damp months. In 

 dry seasons the seedlings infected have a blackened, scorched 

 appearance. 



Infection primarily takes place by means otovtspores (oospores] 



