3^4 
THALLOPHFTES. 
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 
ascQgenous hyfh(E. 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 
Ipwer 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- 
holus furfur aceus {cf. p. 309), it may be assumed that the tubular hyphse 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.] 
