272 DR. LAUDER LIKDSAY ON ARTIIOKIA MELASPERMELLA. 



two or three species, but I occasionally met with as many as 

 tlivee forms ofspermogone in the same species — an instructive illus- 

 tration of polymorphism in the fructification of Lichens^ a sub- 

 ject of such physiological interest that I purpose returning to it 

 in detail, and devoting thereto a special essay. 



Externally the pycnides o^ Artlionia resemble the.spermogones 

 in being very minute, brown or black, punctiform papilla), partly 

 immersed, scattered over the thallus and among the apothecia. 

 They occurred, for instance, in the following species : — 



I. Arthonia astroideaj Ach., var. Swartziana, Acli/ (PL VI. 

 figs. 9, 10.) 



1. Specimens in my Herbarium from Grreat Island, Cork : 

 Carroll (fig. 9). The thallus here is white and smooth, bounded 

 by a black, irregular hypothallus. The pycnides are thus pro- 

 minent as largish, irregular, black cones, scattered abundantly 

 outside the region of the apothecia, much larger than the spermo- 

 gones of the same species. The stylospores (fig. 9, c) are brown, 

 irregular in form, which is generally ellipsoid or oblong, some- 

 times obovate, pyriform, or curved, about *00015 inch long, and 

 •000075 broad : borne on the apices of short, simple sterigiuata, 

 about '00045 long (a). 



2. On ash about Belp, Switzerland : Schajrer, Exs. 463 (fig. 10). 

 Here the pycnides occur as small black dots or points, in groups 

 among the apothecia. The envelope or perithecium, like that 

 of the spermogone of the type (fig. 11, a), consists of deep-brown, 

 very small, closely aggregated cells. The sterigmata (a, b) are 

 brown, short, simple, linear (a), sometimes branching or spread- 

 ing below (b) [as in lAchina pygmcea^ Ag., examined by me in 

 Leighton's Exs. 260], varying in length from '00045 to "00025 inch. 

 They bear on their apices pale-brown stylospores (c), oval or 

 ellipsoid, sometimes pyriform, about '00006 broad, varying m 

 length from '00015 to -00038. In specimens occurring on Finns 

 j}icea on Mount Gurten, Switzerland (Schaer. Exs. 634), I found 

 conceptacles of similar external characters, which seem to be the 

 pycnides of an accompanying very minute Sphceria^ whose pori- 

 thecia may be confounded with the pycnides or spermogones of the 

 Arthonia. The perithecia of the Sphceria are distinguished, how- 

 ever, by their containing sac-like polysporous thecae ; while the 

 stylospores of the pycnides are very small, ellipsoid, simple, and 

 brown. 



brown. 



The spermogones of the type A. astroidea (fig. 11), possess 



very short, simple sterigmata (J), and generally atomic, oval or 



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