Ilcathfield, who found it succeed. I now may, therefore, 

 venture to give my opinion*. 



By my advice, Lord HeatJifield caused proper passages for 

 the admission of common dry air, whicli became an effectual 

 cure, and, I persist in it, that where there is a certain pro- 

 portion of dry air, these Fungi are not to be found, but only 

 in those seasons when such is natural to the climate. They 

 indicate a certain temperature, like a thermometer, pointing 

 it out wlien we otherwise do not perceive it ; and we may be 

 assured, that a certain degree of moisture and temperature is 

 as necessary for the growth of the Fungus tribe, as any other. 

 The ancients were aware of the effects of certain winds being 

 more or less wholesonse ; and the architects advised the build- 

 ings in the streets to be placed accordingly ; and when foetid 

 lakes or any other reasons occurred, to avoid the ill effects 

 Avith what care they could. 



Tab. 409. On June 1 7, 1807, John Walker, Esq. sent me 

 specimens of the leaves from some wall trees, at his seat at 

 Southgate, on the surface of which grew the present parasite. 

 It covered nearly in this manner a large number of trees. 

 The individual leaves did not appear much affected around it. 

 The yellow margin of the Fungus succeeding the green of the 

 leaves, passes into an orange-colour, on which are numerous 

 bluntish conical projections, often emitting from their centre 

 an orange substance, of a jelly-like appearance, and looking 

 very much like little volcanos; some seem riper, and are 

 nearly black, and the substance at the mouth appears de- 

 cayed and whitish; and from the transverse section we might 

 suppose them to belong to the Genus Spha^ria, the inside 

 filled more or less witli this substance, forming, from the 

 centre in the upper half of the leaf, while the cuticle and 

 cortex forms the orange or black conical covers; the under 

 side of the leaf is apparently perfect and not at all disturbed. 

 Mr. Walker had the leaves stripped from the trees. 



* Vitriol of iron or sulphate of Iron, and other means had been used without' 

 success ; drying stores had also been tried, but for v.ant of caution as io the simple 

 means of eradicating the damps, by admitting sufficient dry air, caused it to flourish. 

 Some person ofTere J to prevent the evil efiects of this Fungus at half a guinea per 

 foot — an handsome price ! 



