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EXPLANATION OF PLATES. 297 
Lichina pygmea, Ag.; Leighton exs., 260. Portion of thallus, showing different forms of 
spermogones @ and 6. 
Portion of thallus of same plant, more highly magnified to show the spermogones a (closely 
resembling apothecia). 
Section of portion of a spermogone : a, cellular envelope ; b, sterigmata; c, cavity of sper- 
mogone full of free spermatia. 
Sterigmata and spermatia of same species, 
L. conjinis, Ag. Apothecia (a) highly magnified, showing the spermogones b, seated 
on their surface ; c, ostiole of apothecia; d, ostiole of spermogones. 
Collema pulposum, Ach. Portion of thallus, showing an apothecium a, and marginal 
spermogones 6. 
C. melenum, Ach. (= C. jacobefolium, Auctt.) Thallus, showing an apothecium a, and 
spermogones which are marginal at b, and sub-marginal at c. 
C. melenum, Ach. Portion of margin of thallus slightly magnified, showing the marginal 
(a) and sub-marginal (b) spermogones. 
One of the discoid marginal spermogones of the same species: a, margin of thallus ; 6, 
body of spermogone ; ¢, ostiole. 
C. nigrescens, Ach. Portion of thallus, showing a, apothecia; 6, papilleform spermo- 
gones. 
Section through an apothecium («) and spermogones (b) of C. nigrescens, Ach. 
C. flaccidum, Ach.; Aghalie Bridge, Ireland, Portion of thallus, showing apothecia a, 
and sub-marginal spermogones 6. 
Leptogium tremelloides, Fr.; Killarney, Ireland. Portion of thallus, showing a, apothecia ; 
b, marginal and sub-marginal spermogones. 
L. tremelloides, Fr.; South America. Portion of margin of thallus, magnified to show the 
denticulate spermogones a; 3, ostiole. 
Sterigmata and spermatia of same species. 
VOL, XXII. PART f. 4q 
