244 MOULDS REFERRED BY AUTHORS TO FUMAGO. 



It is well known that the leaves of various trees are frequently 

 more or less covered with a black sooty or velvety stratum, to 

 the great detriment of their beauty, and frequently of their health 

 and productiveness, by choking up the stomates, and thereby 

 preventing the access of the atmospheric air to the tissue of the 

 leaves. A case of this kind, which occurred in Ceylon on coffee, 

 was a short time since noticed by one of us in this Journal ; 

 the orange trees in the Azores and Madeira have of late most 

 grievously suffered from a similar affection ; and Dr. Montagne 

 has very recently given an account of an extensive disease of this 

 description amonj^st the olive trees in the neighbourhood of 

 Perpignan in 1829. Not only the leaves but the branches were 

 more or less covered, and the harvest was materially affected. 

 Similar growths are common on the leaves of plum, lime, hazel, 

 rose, &c., and on the different species and varieties of the genus 

 citrus in our conservatories. They are often, if not always, 

 preceded by honey-dew, whether arising from aphides or from 

 a sugary excretion from the leaves themselves ; frequently too 

 they are accompanied by some species of coccus, especially in 

 the genus citrus. However similar they may be in outward ap- 

 pearance, the parasites by which these diseases are produced differ 

 materially in structure ; in some the characters are so singular, 

 that we have thought some account of the particular group by 

 which they are exhibited may not be uninteresting. 



A portion of these plants consists of species of the genus 

 A?itennaria, as that of the olive mentioned above, specimens of 

 which were gathered by Dr, Scouler in Portugal, in 1846. 

 Others occur commonly on heath, on different species of cistus, 

 on the Scotch fir, &c. One veiy highly developed form, rising an 

 inch or more from the surface, and investing whole plants with 

 a spongy mass, is found in the islands of the southern hemisphere 

 and in South America ; another species frequently covers the 

 leaves of the ferns in Juan Fernandez ; and one has been lately 

 sent by Mr. Curtis from South Carolina on the leaves of Kalmia 

 latifolia, which appears to be identical with an undescribed 

 species gathered by Mr. Broome in the west of England on the 

 leaves of the sycamore. Persoon distinguished these from other 

 analogous productions on leaves, as Link and Nees von Esen- 

 beck had done previously, but, without adopting their notions, 

 he referred them to the genus Torula. The views, however, of 

 the German mycologists have been confirmed by more recent 

 observers, and the genus Antennaria still holds its place. 



Other forms were separated by Persoon under the generic 

 name Fumago, of which he made two sections. It is with the 

 second of these, distinguished by the name of Polychceton, that 

 we are principally concerned at present. The first consists in 



