DR LAUDER LINDSAY ON NEW LICHENICOLOUS MICRO-FUNGI. 519 



change from mutual pressure. Their colour is usually in maturity and age a deep 

 blackish-brown ; but in the young state they may be pale, or even colourless ; 

 while in older conditions they may be olive, with a blackish tinge. When aggre- 

 gated in groups of two, if the form of the constituent spores remains compara- 

 tively regular, they may be indistinguishable from some figure-8-shaped lichen or 

 fungus-sporidia. Hence, in one case, among the parasites hereinafter described 

 (the Mangerton plant),* it is difficult to determine whether it is Coniothecium 

 lichenicolum or a separate parasite. Sometimes the spores are concatenate, 

 as in Torula ; but they are at once distinguished from those of Torula by their 

 breadth being greater than their length, as well as by their sub-cubical form. 

 When in aggregates of four, the spore-groups resemble wool-pack-like or Sarcina- 

 like cubes. When in threes, as well as sometimes in twos or fours, they are very 

 unlike spores, and are apt to be mistaken for fragments of cellular tissue, such 

 as that which constitutes the perithecium of many of the lower lichens and 

 fungi.f Whether simple or aggregate, the spores always exhibit double contour, 

 presenting the aspect of being thick-walled. The Coniothecium may be scattered, 

 as it generally is, or grouped ; very rarely it is closely aggregated or even con- 

 fluent. The thallus, which it affects, is frequently so altered— apart, however, 

 from the growth of the parasite — that, in the absence of apothecia, it is impossible 

 to determine the species to which it is referable. It appears generally, if not 

 always, to belong to Lecanora, and, at least frequently, to the species tartarea, 

 parella, and glaucoma. 



3. Genus Microthelia. 



The parasites, which I have provisionally grouped in this pseudo-genus, \ are 

 confessedly most diverse in character, though they possess certain characters in 

 common. For the reasons elsewhere set forth,§ I think there is an advantage 

 in considering them as a group until their characters are more fully known and 

 understood. Their common or general characters are the following : — 



Most of them are microscopic, like Torula; black, papillseform or punctiform. 

 The papillseform or verrucarioid condition is always rendered more distinct by 

 moisture. Sometimes they are flattened and discoid, lecidioid or arthonioid (e.g., 

 the parasites on Lichen dactylinus, Lecidea pachycarpa, and L. albo-atra). Some- 

 times they are maculseform ab initio (e.g., the parasites affecting Squamaria crassa 

 and S. saocicola); at other times the maculse are produced by the confluence or 

 aggregation of minute papillee (as in the parasite affecting Parmelia perlata). 



* (b) P. 540. 



f I have seen true Lichen-sporidia by cohesion acquiring characters closely resembling those 

 concatenate and woolpack-like forms of the spores of Coniothecium lichenicolum (pi. xxiii. fig. 28), e.g., 

 in Lecidea dubia, T. and B., Leight. Exs. No, 88. In several other cases, I have met -with Lichen- 

 sporidia cohering in such manner as to resemble cellular tissue, e.g., in Verrucaria subalbicans, 

 Leight. Exs. No. 200. 



% Vide p. 515, and foot note %. § " Otago Lich. and Fungi," p. 436. 



