148 MICROSCOPIC FUNGI. 



the Eev. M. J. Berkeley^ in 1846, and to which, 

 even now, nothing of importance can be supple- 

 mented or abstracted : — " The leaves began sud- 

 denly to assume a paler, and at leng*th a yellowish 

 tint, exhibiting here and there discoloured spots. 

 More or less coinciding with these spots, on the 

 reverse of the leaves, appeared white mealy patches, 

 consisting of a- minute mould, proceeding, either 

 singly or in fascicles, from the stomata, and arising 

 from an abundant branched mycelium creeping in 

 every direction through the loose tissue beneath 

 the cuticle. The upper surface rarely, if ever, 

 exhibits the mould, it being almost physically im- 

 possible for its dehcate threads to penetrate the 

 closely-packed cells which, being arranged side by 

 side, leave scarcely any intercellular passages. The 

 mould, in a few hours from its first piercing the 

 apertures of the stomata, perfects its fruit, and in 

 so doing completely exhausts the matrix, which in 

 consequence withers. No sooner have a number 

 of the leaves been attacked, than the stem itself is 

 subject to change, becoming spotted here and there 

 with dark brown patches, in which the cells are 

 mostly filled with a dark grumous mass, without 

 exhibiting any mucedinous filaments ; though, occa- 

 sionally, I have ascertained their presence. Very 

 rarely fractifying but dwarfed specimens of the 

 mould occur upon it. The stem now rapidly putre- 

 fies, the cuticle and its subjacent tissue become 

 pulpy, and separate when touched from the woody 



