324 THALLOPHVTES. 



Lichens, beneath the cortical layer, in the lower part of the gonidial zone, or, in some 

 crustaceous Lichens, in the deepest part of the thallus in immediate contact with the 

 substratum; in homoiomerous gelatinous Lichens and in Ephebe it arises beneath the 

 surface of the thallus. The commencement of the apothecium is, in heteromerous 

 Lichens, a very small roundish ball of confused interwoven hyphae, on the outer side 

 of which a tuft of very delicate hyphae — the first paraphyses — rises at a very early 

 period. The most external hyphal investment of this ball, and therefore surround- 

 ing the tuft of paraphyses and opening above (outwards), is termed by lichenologists 

 the Excipulum. The further growth of the rudiment of the apothecium is now 

 occasioned by the increase in size of the excipulum by the formation of new fibres, 

 while new paraphyses are intercalated among those already formed and outside the 

 tuft, the extension of the apothecium being the immediate result of the fresh forma- 

 tion of these bodies. Growth is. first completed in the centre of the apothecium ; 

 at the outside it continues longer, often even after the appearance of the apothecium 

 above the surface of the thallus. The mother-cells of the spores, the asci, are formed, 

 according to Schwendener and Fuisting, in a peculiar manner. ' Even in the young ball, 

 and among the first rudiments of the paraphyses, thicker hyphae are to be seen inter- 

 woven among the rest, rich in protoplasm, undivided by septa, and with numerous 

 ramifications ; the upright ends of the branches of these hyphae which penetrate between 

 the ends of the paraphyses develope into club-shaped asci ; they may hence be termed 

 ascogenous hyphoe. They are very readily distinguished from the paraphyses by their 

 membrane being coloured blue by iodine after treatment with potash-solution, while 

 that of the paraphyses remains colourless. They disappear at a very early period from 

 the lower part of the rudiment of the apothecium, and remain only in one narrow layer 

 which runs parallel to the upper surface of the apothecium, and extends below the 

 lower ends of the ripe asci. In this layer they ramify in a centrifugal direction in 

 proportion as the margin of the excipulum grows, and send out new asci among the new 

 paraphyses. The first asci appear in the centre of the apothecium ; and Schwendener 

 states that no genetic connection exists between the ascogenous hyphae and those from 

 which the paraphyses are derived; the two form separate systems but interwoven 

 into one another^. The layer in which the ascogenous hyphae run is called the Sub- 

 hymenial Layer; the hymenium itself consists of the paraphyses and the asci taken 

 together. The term Hypothecium is given to the mass of fibres which lies beneath the sub- 

 bymenial layer, and is often strongly developed through subsequent growth ; it consists 

 of hyphae the branches of which end in the hymenium as paraphyses, and of the remains 

 of the primary ball ; when mature, it can scarcely be distinguished from the excipulum. 

 The growing apothecium bulges more and more, and finally breaks through the 

 layer of thallus which covers it; the hymenium and the margin of the excipulum 

 appear above the surface of the thallus, or the part of the thallus which surrounds 

 the excipulum rises and grows with it forming a bowl-like rim. Among the medullary 

 hyphae which surround the apothecium a number of gonidia subsequently appear in 

 many Lichens, so that a gonidial layer runs beneath the apothecium. In Peltigera and 

 Solorina even the young apothecium is expanded flat, its paraphyses project vertically 

 towards the surface of the thallus, and the layer of thallus which covers them is finally 

 'lifted like a thin veil. In Bceomyces, Calycium, &c. the basal portion of the hypothecium 

 is developed into a long stalk which supports the apothecium. 



' From the newly-discovered processes in the formation of the reproductive organs of the 

 Pyrenomycetes and Discomycetes, especially from the most recent statements of Janczewski on Asco- 

 bolus furfuraceu& {cf. p. 309), it may be assumed that the tubular hyphae of the sub-hymenial 

 layer arise from a yet undiscovered ascogonium or scolecite ; and that thus the apothecium of 

 Lichens is the result of a sexual process in a similar manner to the perithecia of the Pyrenomy- 

 cetes and the apothecia of Peziza and Ascobolus. [This has been discovered by Stahl. See the end 

 of this section.] 



1 



