172 FUNGOID PESTS OF CULTIVATED PLANTS. 



retain, although evidently wrong, as it is not a Leptothyrium at all. He 

 says : " It begins on the young leaves, causing a brownish ill-defined spot ; 

 after a time this exhibits different shades of olivaceous-brown, and the 

 parenchyma of the leaf becomes quite pulpy and semi-putrescent. On 

 the underside of the leaf little raised dots are seen, which are caused 

 by the cysts of a fungus beneath. The parenchyma is more or less 

 traversed by hyaline mycelium with jointed threads, and each cyst or 

 perithecium, which is of a pale umber, is surrounded by a broad border of 

 hyaline, perfectly colourless, jointed threads, the upper joints of which 

 are more or less swollen. 



" Sometimes the leaves pass rapidly into a state of decay, but occa- 

 sionally the parenchyma dries up, the spots become bleached, but are 

 surrounded by a dark border and studded with the concentrically arranged 

 perithecia. In these I have detected spores, which are broader at one 

 end than the other, and uniseptate. Occasionally the disease commences 

 again in the same leaf, so that the incipient and old stages may be com- 

 pared together." 



These examples were found on the leaves of Ly caste Skinneri and on 

 Odontoglossum citrosmum. 



" The fungus is in all probability merely a condition of some more 

 perfect form, to which the provisional name of Leptothyrium perniciosum 

 may be given. 



" Spots at first olivaceous-brown, at length bleached ; perithecia at 

 first scattered, at length somewhat concentric, depressed, surrounded by 

 a fringe of hyaline articulated colourless threads. Spores with two 

 nuclei, obovate oblong, sometimes at length uniseptate. 



" It is not a good Leptothyrium ; on the thin leaves of Lycaste it looks 

 much more like. In this case the spots are sometimes six inches long, 

 and parallel to each other, following the direction of the nerves." 



We have never seen this species, but insert it in the hope that some 

 knowledge may be obtained. There are features which lead to the con- 

 clusion that it may be a Gl&osporium or Marsonia, which is far more 

 probable than Leptothyrium. 



Journ. E.H.S. vol. i. N. S. 1866, p. 25. 



OKCHID BLACK MOULD. 

 Cladosporium Orchidearum (C. & M.), PI. XV. fig. 29. 



There need be no alarm amongst Orchid-growers respecting this new 

 form of parasite which falls upon decaying leaves, since we are convinced 

 that it only makes its appearance on dead or diseased tissue. 



The threads are in tufts which seem to protrude through the stomata, 

 and are short, here and there branched and septate, but slender and 

 flexuous, and of a pale olive colour. The spores or conidia are borne at 

 the tips of the branches, and are mostly elliptical, with a cross division in 

 the centre forming two cells (17-18 x 5-6 /u) of a pale olive colour. The 

 conidia are very variable in this genus, both in size and form, some being 

 found without a division and others with two or three, but in the present 

 instance we have observed none with more than one division. 



Gard. Chron. Oct. 11, 1890, fig. 82 ; Sacc. Syll. x. 7506. 



