278 PHYLOGENY 



Reinke has indicated the course of evolution within the series but that 

 is on the Hnes of thalline development and will be considered later. 



c. Graphidineae. This series contains a considerable variety of lichen 

 forms, but all possess to a more or less marked degree the linear form of 

 fructification termed a " lirella " which has only a slit-like opening. There 

 is a tendency to round discoid fruits in the Roccellae and also in the Arthoniae; 

 the apothecia of the latter, called by early lichenologists "ardellae," are with- 

 out margins. In nearly all there is a formation of carbonaceous black tissue 

 either in the hypothecium or in the proper margins. In some of them the 

 paraphyses are branched and dark at the tips, the branches interlocking to 

 form a strong protective epithecium. There are, however, constant exceptions, 

 in some particular, to any generalization in genera and in species. Miiller- 

 Argau's^ pronouncement might be held to have special reference to Graphi- 

 dineae: "that in any genus, species or groups of species are to be found 

 which outwardlyshew something that is peculiar, though of slightimportance." 

 The most constant type of gonidium is Tretitepohlia, but Palmella and 

 Phycopeltis occasionally occur. The spores are various in colour and form ; 

 they are rarely simple. 



The genus Arthonia is derived from a member of the Patellariaceae, from 

 which family many of the Discomycetes have arisen. The course of develop- 

 ment does not follow from a closed to an open fruit ; the apothecium is open 

 from the first, and growth proceeds from the centre outwards, the fertile cells 

 gradually pushing aside the sterile tissue of the exterior. The affinity of 

 Xylographa (with Palmella gonidia) is to be found in Stictis in the fungal 

 family Stictidaceae, the apothecia of Stictis being at first closed, then open, 

 and with a thick margin ; 'Xylographa has a more elongate lirella fruit, though 

 otherwise very similar, and has a very reduced thallus. Rehm" has classified 

 Xylographa as a fungus. 



The genera with linear apothecia are closely connected with Hysteriaceaej 

 and evidently inherit their fruit form severally from that family. There is 

 thus ample evidence of polyphyletic descent in the series. Stromatoid fruits 

 occur in Chiodectonaceae, with deeply sunk, almost closed disc, but they 

 have evidently evolved within the series, possibly from a dividing up of the 

 Hrellae. 



In Graphidineae there are also forms, more especially in Arthoniaceae, 

 on the border line between lichens and fungi: those with gonidia being 

 classified as lichens, those without gonidia having been placed in corre- 

 sponding genera of fungi. These latter athalline species live as parasites or 

 saprophytes. 



The larger number of genera have a poorly developed thallus; in many 

 of them it is embedded within the outer periderm-cells of trees, and is known 



^ Miiller-Argau 1863. '^ Rehm 1890. 



