41 
sporidia are smallish. The perithecia and sporidia alike are so 
different from the apothecia and sporidia of the Lecidea that 
the former are probably to be regarded as parasitic, holding a 
similar relation to L. petrea that (e.g.) Pertusaria paradoxa, 
Linds.,!does to Lecanora oculata. In this case the parasite may 
be provisionally distinguished as Microthelia petreicola. The 
only other permissible conclusion is that the perithecia in 
question are a secondary form of sporidiferous fructification 
belonging to the Lecidea, in which event the phenomenon 
would be physiologically and morphologically even more 
interesting. 
11. On Lecidea geographica, L. 
(a) Var. atro-virens, Sch., on granite, St. Moritz, in 
Hepp’s Exs., No. 153. Some of the thalline areole are 
studded over with a parasite, which is probably Ticho- 
thecium stigma, Korb. (Parerga, p. 468).2 It occurs as 
microscopic, black, round, punctiform conceptacles, gene- 
rally immersed, sometimes sub-papillar, containing a hyme- 
nium and asci that give a blue or violet colour with iodine, 
the said blue being more easily and rapidly developed in the 
hymenial gelatine than in the asci. Paraphyses indistinct. 
Asci, 8-spored. Sporidia intermixed, as usual, with oil-globules ; 
colourless, or nearly so, in the young state (in the asci) 
gradually assuming an olive or brown colour ; oval or ellipsoid, 
in maturity 2-locular, sometimes with a constriction opposite 
the septum; in the young state sometimes simple, or the 
septum obscure; in all stages of growth granular. In this 
parasite the sporidia are much larger than those of some 
forms at least of L. alpicola. ‘There can generally be no con- 
fusion with the sporidia of L. geographica, which in its 
common form are very large and muriform.* 
The spermogonia, however, of L. geographica (var. atro- 
virens, as I have examined them in Hepp’s Exs., No. 153, 
Scheerer’s Exs., No. 623, and Mougeot and Nestler’s Exs., 
No. 640) are externally indistinguishable from the parasite 
above described. ‘They are of less common occurrence, gene- 
rally very rare, and are scattered (when they do occur) in 
groups over some of the sterile thalline areole, as black, 
_ punctiform conceptacles, conspicuous from the contrast of 
colour. Their walls consist of brown cellular tissue. The 
1 “Observations on W. Greenland Lichens,” pp. 344 and 366, plate |, 
g. 5. 
 [bid., p. 367, plate li, fig. 12. 
3 Jbid., p. 367, plate lii, figs. 4, 5, 6, and 13. 
4 Ibid., pp. 367-8, plate lii, figs. 7, 8, and 9. 
