FUNGOID PESTS OF FOREST TREES. 



363 



Sycamore White Mould. 

 Botrytis deprcedans (Cooke), PI. XIX. fig. 4. 



First discovered on living leaves of Acer Psendo-Platanus in a damp 

 wood. Several young trees had nearly every leaf affected, and the next 

 year they were dead. Greyish spots were formed on the leaves, which 

 were sometimes large and confluent. The threads were flexuous and 

 septate, simple, crowned at the apex with elliptical basidia-like cells, 

 ultimately two-lobed. The glomerules of conidia globose and compact. 

 Conidia globose, 12// diam. 



After the leaves had fallen to the ground, and lain for a short time, 

 numerous minute black sclerotia were formed, the ultimate development 

 of which was never ascertained. 



Certainly a most destructive pest, but it does not appear to have been 

 recognised elsewhere, at home or abroad. This parasite has never been 

 thoroughly investigated, and, as it has occurred so seldom, there has been 

 no opportunity for experiment on remedies. 



Sacc. Syll. iv. 691 ; Cooke, Journ. Q.M.C. ii. 1885, p. 138, t. x. f. 4. 



In damp years Maple seedlings are liable to destruction by a black 

 mould, Cercospora acerina. 



Hart. & Som. Dis. Trees, p. 135. 



Sycamore-Leaf Blotch. 

 Bhytisma acerinum (Fr.), PI. XIX. fig. 5. 



The large black pitchy-looking blotches on the leaves of Sycamore 

 and Maple are so common and so well known that they scarcely need 

 description. Sometimes nearly every leaf on a tree is infected, and then 

 considerable injury must be caused by preventing the leaves performing 

 their proper functions. 



Whilst still attached to the tree the fungus remains in its first stage . 

 The patches are yellow when they first appear about June, soon changing 

 to black and corrugated. Within this stroma are cells, or cavities, in which 

 the conidia are produced, which are narrow and curved (6-9 x 1 /*). In 

 this stage it is known as Melasmia acerina. 



After the leaves have fallen to the ground and passed the winter a 

 second stage or condition is reached, in which the contents of the cells or 

 cavities in the stroma are occupied by sporidia contained in asci. This is 

 the true Bhytisma stage, and the sporidia are matured in the spring . 

 These sporidia are needle-shaped (60-80 x 1^-2^ n) and uncoloured. 



Known also in France, Germany, Balgium, Sweden, Finland, Italy, 

 and North America. 



So long as the leaves are permitted to remain on the grou nd, and 

 perfect the fruit of the parasite, it will remain as a pest. 



Sacc. Syll. iii. 3390, vii. 3083 ; Mass. PL Dis. 142, fig. 28 ; Cooke, 

 Hdbk. No. 2279; Grev. Sc. Cr. FL t. 118, f. 1; Hart. & Som. Dis. 

 Trees, p. 105, fig. 50. 



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