166 REPRODUCTION 



formed a wide-stretching hymenium. Several carpogonia took part in the 

 formation of one apothecium. 



The tissue below the ascogonium meanwhile developed vigorously, form- 

 ing a weft of encircling hyphae, while the upper branches grew vertically to- 

 wards the cortex. Gonidia in contact with the developing fruit also increased, 

 and, with the hyphae, formed the exciple or thalline margin. The growth 

 upward of the paraphyses raises the overlying cortex which in Anaptychia 

 is " fibrous "; it gradually dies off and allows the exposure of the disc, though 

 small shreds of dead tissue are frequently left. In species such as those of 

 Xanthoria where the cortex is of vertical cell-rows, the apothecial hyphae 

 simply push their way between the cell-rows and so through to the open. 



Baur found the development of the apothecium somewhat similar in the 

 crustaceous corticolous lichen, Lecanora subfusca. After a long period of 

 sterile growth, spermogonia appeared in great abundance, and, a little later, 

 carpogonia in groups of five to ten ; the trichogynes emerged very slightly 

 above the cortex; they were now branched. The ascogonia were frequently 

 a confused clump of cells, though sometimes they showed distinct spirals. 

 The surrounding hyphae had taken a vertical direction towards the cortex 

 at a still earlier stage, and the brown tips were visible on the exterior before 

 the trichogynes were formed. The whole growth was extremely slow. 



In Physcia stellaris the carpogonia occurred in groups also, though Lin- 

 dau 1 thinks that, unlike Anaptychia (Physcia) ciliaris, only one is left to form 

 the fruit. Only one, according to Darbishire 2 , entered into the apothecium 

 in the allied species, Physcia pulverulenta. In the latter plasma connections 

 were visible from cell to cell of the trichogyne, and, after copulation with 

 the spermatium, the ascogonial cells increased in size though not in number 

 and the plasma connections between them became so wide that the asco- 

 gonium had the appearance of an almost continuous multinucleate cell or 

 coenogamete 8 . As in gelatinous lichens, each of these cells gave rise to 

 ascogenous hyphae. 



c. GENERAL SUMMARY. The main features of development described 

 above recur in most of the species that have been examined. 



(l) The carpogonia arise in a complex of hyphae situated on the under 

 side of, or immediately below the gonidial zone. Usually they vary in number 

 from five to twenty for each apothecium, though as many as seventy-two 

 have been computed for Icmadophila ericetorum*, and Wainio 8 describes 

 them as so numerous in Coccocarpia pellita var., that their trichogynes covered 

 some of the young apothecia with a hairy pile perceptible with a hand lens, 

 though at the same time other apothecia on the same specimens were 

 bsolutely smooth. 



1 Lindau 1888. 2 Darbishire 1900. * See also p. 180. 4 Nienburg 1908. 5 Wainio i. 1890. 



