Vol,. 1] Reed. — Two New Ascomycetous Fungi. 159 



the transformation of the Prasiola is much more striking, and 

 the structure more closely approaches that of the ordinary lichen • 

 Here the relation seems much more like that of a lichen fungus 

 to its gonidial alga, than of an ordinary parasite. The fronds of 

 the Prasiola-composite are entirely different from the normal 

 Prasiola in structure, as well as in general appearance. The 

 peculiar manner in which the cells divide in three planes and form 

 "tetrads," thus enormously thickening the frond, certainly sug- 

 gests the lichen formation. The fact that the "tetrads" are so 

 entirely isolated and so widely scattered also suggests the distribu- 

 tion of lichen gonidia in the thallus. Likewise the density of the 

 interwoven mycelium and the pigmentation of the outer layer with 

 the numerous irregularly scattered perithecia, still further estab- 

 lishes the belief that it is a lichen. It seems very probable that 

 this Prasiola is the gonidia of a lichen fungus, which surrounds it 

 and associates with it very much in the same way as in Reinsch's 

 Dermatomeris and Hooker's Mastodia. The Prasiola-composite 

 resembles both the Mastodia and Dermatomeris in several 

 important details; as the isolated "tetrads," the perithecia, and the 

 dense mycelium separating these cells forming the "tetrads," as 

 well as the general habit of the ])lant. Indeed they are so much 

 alike in both structure and habit, that if Reinsch is correct in his 

 classificatioa of Dermatomeris, this Prasiola-composite should be 

 classed with them as an endocarpous lichen. The Mastodia, 

 which is also a Prasiola-composite, is a fresh water species and 

 differs in several details of structure, if Hooker's figures are 

 correct. They are much alike in surface view, but in cross 

 section Hooker's figures show only a single layer of algal cells. 

 The interweaving mycelium does not show, but only the peri- 

 thecia, while Harlot's figures show all these details and resemble 

 ours quite closely. Perhaps the Ulva composite should also be 

 classed in this same group, though it is much less distorted and 

 transformed by the fungus than the Prasiola, and resembles a 

 lichen much less, both in external appearance and structure. 

 Yet in spite of these differences these four composites are 

 undoubtedly closely related and seem to approach the true lichen 

 structure. It seems best, however, in view of the later ideas 

 concerning lichens, to describe them simply as composites of 

 merely parasitic relationship. 



