BRITISH LICHENS. 19 



BRITISH LICHENS : HINTS HOW TO STUDY THEM. 



BY W. PHILLIPS, F.L.S. 



Read before the Society, March gth and 2,0th, 1880. 



The group of plants classed as Lichens, though for the most part 

 minute in stature, offer a highly interesting held of study to the lover of 

 nature, and will well repay the labour bestowed upon them by px-esenting 

 before the mind much beauty of form and curiosity of structure. To him 

 who wants an inducement to seek the country lane, the wooded park, or 

 the breezy hill side, no better one can be found than in the pursuit of 

 these attractive little plants, which need no care in drying, and httle 

 space for storing. The thousands of species that he scattered on the 

 surface of old trees, the face of weathered rocks, and on heathy pastiu'es, 

 will supply an exhaustless source of pleasure to the man who is capable 

 of appreciating the wisdom of the gi'eat Creator, displayed in the lower 

 forms of vegetable life ; nor is there that difficulty in their study which 

 some people have imagined. As in other departments of botany, as indeed 

 in every branch of human knowledge, there are cexiiain initial difficulties — 

 those which stand on the threshold of the subject — which give some 

 trouble, but when these are siu'mounted the course becomes easy and 



References to Plate V. 



Fig. l.—Cetraria Islandica, a single frond, natural size. 



Fig. 2.—Sph(Brophoron coralloides, natural size, a, apothecium, 



Fip. S.—Usnea barbata, natural size; a, apothecium. 



Fig. A.—Physcia parietina, natural size on wood ; a, apothecia. 



Fig. 5. — Placodiumcallopismum, a portion of a specimen, natural size, 



Fie. 6. — Squamaria crassa, natural size. 



Fig. 1 .—Lecidea geographica, natural size. 



Fig. 8. — Graphis elegans, natural size. 



Fig. 9. — Perpendicular section of the tballus of Physcia parietina, much 



magnified ; showing the three strata, a cortical layer, b gonidlal 



layer, c medullary layer. 

 Fig 10.— Perpendicular section of the thallus of a Leptogium, much 



magnified ; showing the intermixed hyphfe and gonidial necklaces. 

 Figs. 11 & 12. — Perpendicular sections of apothecia of Physcia parietina, 



very Uttle magnified ; the first a young, the second an older indi- 

 vidual. 

 Fig. 13. — A perpendicular section of the same, more highly magnified ; a 



asci with sporidia, b paraphyses, c hypothecium. 

 Fig. 14.— Perpendicular section of a spermagonium immersed in the 



thalius, highly magnified ; a ostiolum, b and c different forms 



of sterigmata, showing the spermatia in situ. 

 Fig. 15.— Perpendicular section of a pycnidium seated on the thallus, highly 



magnified ; a ostiolum, b basidia and spores, c detached spores 



more highly magnified. 

 Fig. 16. — Spores of Physcia parietina, highly magnified. 

 Fig. 17.— Perpendicular section of a lecideine apothecium, slightly magnified. 

 Fig. 18.— Perpendicular section of a dimidiate peridium of a Verrucaria, 



sUghtly magnified. 

 Fig. 19. —Perpendicular section of a peridium of a Crraphis, showing the 



dimidiate form, slightly magnified. 

 Fig. 20.— Perpendicular section of an entire peridium of an Opegrapha, 



sUghtly magnified. 

 Fig. 21.— A perpendicular section of an apothecium immersed in the thallus, 



slightly magnified. 



