In Physcia stellaris the carpogonia occurred in groups also, though Lindau[567] thinks that, unlike Anaptychia (Physcia) ciliaris, only one is left to form the fruit. Only one, according to Darbishire[568], 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 ascogonium had the appearance of an almost continuous multinucleate cell or coenogamete[569]. 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.
(1) 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[570], and Wainio[571] 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 absolutely smooth.
(2) The trichogynes, when present, travel up through the gonidial and cortical regions of the thallus; Darbishire[572] observes that in Physcia pulverulenta, they may diverge to the side to secure an easier course between the groups of algae. They emerge above the surface to a distance of about 15µ or less; after an interval they collapse and disappear. Their cells, which are longer and narrower than those of the ascogonium, are uninucleate and vary in number according to species or to individual lichens. Baur[573] thought that possibly several trichogynes in succession might arise from one ascogonium.
(3) How many carpogonia share in the development of the apothecium is still a debated question. In Collema only one is functional. Baur[574] was unable to decide if one or more were fertilized in Parmelia acetabulum, and in Usnea Nienburg[575] found that, out of several, one alone survived ([Fig. 95]). But in Anaptychia ciliaris and in Lecanora subfusca Baur[574] considers it proved that several share in the formation of the apothecium. In this connection it is interesting to note that, according to Harper[576] and others, several ascogonia enter into one Pyronema fruit.
Fig. 95. Usnea barbata Web. Carpogonium with trichogyne × 1100 (after Nienburg).
(4) The ascogonial cells, before and after fertilization, are distinguished from the surrounding hyphae by a reaction to various stains, which is different from that of the vegetative hyphae, and also by the shortness and width of their cells. The whole of the apothecial primordium is generally recognizable by the clear shining appearance of the cells.
(5) The ascogonia do not always form a distinct spiral; frequently they lie in irregular groups. Each cell is uninucleate and may ultimately produce ascogenous hyphae, though in Anaptychia Baur[574] noted that some of the cells failed to develop.