REV. M. J. BERKELEY — ON A PARASITIC EUNGUS. 27 



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

 sionally the parenchym 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 and uniseptate. Occasionally, as in the case 

 represented in our figure, the disease commences again in the 

 same leaf; so that the incipient and old stages may be compared 

 together. I have since had an opportunity of studying the fungus 

 in an intermediate condition on Lycaste SMnneri, and have seen 

 the spores seated on their sporophores. 



It is extremely important that this form of spot should be ac- 

 curately distinguished from the other forms, and I trust that the 

 figures now given will enable any accurate observer to distinguish 

 it, even without having recourse to the microscope. In the case 

 of such a minute plant the cultivator cannot be expected to verify 

 every point, and the distinction of mycelium amongst tissue is 

 often a matter of considerable difficulty. 



Our figure (1) represents a leaf of Odontoglossum citrosmum 

 attacked by the fungus in an incipient stage at a, and past ma- 

 turity at b. At c appears a form of spot which, though unsightly, 

 is not destructive like the form which is characterized by a multi- 

 tude of pale pits. 



Fig. 2 is a magnified representation of one of the cysts sur- 

 rounded by its broad fringe. 



Fig. 3 gives the spores, which are about ^o^ th of an inch long, 

 seated on their sporophores and free, magnified. 



Fig. 4 represents a portion of the mycelium magnified. 



The fungus is in all probability merely a condition of some 

 more perfect form ; but it may be well, in the present transitional 

 state of the part of mycology to which it belongs, to give it a 

 provisional name, and it may therefore be called Leptothyrium 

 perniciosum, and characterized : — Spots at first olivaceous brown, at 

 length bleached j perithecia at first scattered, at length somewhat 

 concentric, depressed, surrounded by a fringe of hyaline articu- 

 lated colourless threads ; spores with two nuclei obovate-oblong, 

 sometimes at length uniseptate. 



It is not, however, a very good ZeptotTiyrium, though the cha- 

 racter in which it departs from the normal form of the genus pro- 

 bably depends merely on the thick condition of the cuticle of the 

 leaves on which it is developed, which prevents the cysts sepa- 

 rating at the base as in other species. On the thin leaves of 

 Lycaste Shinneri it looks much more like a Zeptothyrium. In this 



