vegetation arising from the germination of the spores, and upon 

 which the several other layers of the thallus are gradually and 

 eventually deposited. This hypothallus is often only perceptible 

 in a dark border around the thallus. The thallus is conspicuous 

 enough in the forms above mentioned, but is often hypophlmodal 

 or concealed beneath the epidermis of the bark on which it grows, 

 or evanescent, existing only in scattered portions on or under the 

 friable face of the rocks, or in other cases altogether wanting 

 when the apothecia grow parasitically on the thallus, or apothecia 

 of other lichens. 



The gonidia are produced in cells of very young thalli and even 

 in older thalli and are of two sorts — either a simple cell contain- 

 ing granular matter termed a gonidium, or clusters of two, three 

 or more spherical granules without any proper cellular membrane, 

 containing green granular matter and named granula gonima. 

 These gonidia, together with the molecular granulations, and fila- 

 ments of the medullary layer, are often protruded through the 

 cortical layer to the surface of the thallus in powdery or granular 

 eruptions of a globular shape termed soredia. 



The apotkecium of whatever form, whether patellulate, lirellate, 

 or enclosed in wartlike perithecia or nuclei, has a similar internal 

 structure, and when viewed in a vertical section is seen to consist 

 of an excipulwm, dark or pale, formed of cells generally compact, 

 subtending the hypothecium, of similar structure, and either 

 dark or colourless, from whose upper surface in an erect position 

 grow the asci or thecoe and the paraphyses constituting the 

 hymenium or thalamium, and are conglutinated by a jellylike 

 mucus termed the gelatina hymenea. The paraphyses are slender 

 filaments having minute globular or clavate apices filled with 

 coloured granular matter, which, by their close proximity, consti- 

 tute the disk or epiihecium, and to which they give their peculiar 

 colour. Around this disk or epithecium is a margin formed by the 

 edges of the excipulum or hypothecium and of the same colour, or 

 else formed by the thallus, and partaking of its peculiar colour. 

 The former is termed a proper margin, the latter a thalline margin. 

 The asci or thecce are linear, clavate, or globular sacs or vesicles 

 containing the spores, which in different species are variable in form, 

 size, and colour, either brown or colourless, simple or divided by 

 septa or otherwise into several cells, and in number generally 8, 

 but sometimes 1, 2, 4, 6, or innumerable. The spores contain 

 either granules or oily nuclei, and have an outer and inner paries 

 or wall termed respectively epispore and endospore. 



The spermogonia are minute globular conceptacles imbedded in 

 the thallus, distinguishable on its surface as minute tubercles, and 

 in section exhibiting a colourless receptacle from which arise 

 minute filaments either simple (sterigmata), or articulate 

 (arthrosterigmata), bearing on their summits or joints very minute 

 rodlike or cylindrical straight or curved bodies (spermatia), which 

 the slightest pressure detaches and protrudes in a cloudy stream 

 through a pore in the apex of the spermogonium. 



