. Lichens. Lichens. REPRODUCTION IN DISCOLICHENS 167. (2) The trichogynes, when present, travel up through the gonidial and cortical regions of the thallus; Darbishire^ observes that in Physcia pulveru- lenta, 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 15/i or less; after an interval they collapse and disappear. Their cells, which are longer and harrower than those of the ascogonium, are uninucleate and vary in number according to species or to individual lichens. Baur^ thought that possibly several
. Lichens. Lichens. REPRODUCTION IN DISCOLICHENS 167. (2) The trichogynes, when present, travel up through the gonidial and cortical regions of the thallus; Darbishire^ observes that in Physcia pulveru- lenta, 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 15/i or less; after an interval they collapse and disappear. Their cells, which are longer and harrower than those of the ascogonium, are uninucleate and vary in number according to species or to individual lichens. Baur^ 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" was unable to decide if one or more were fertilized in Parmelia acetab?dutn, and in Usnea Nienburg^ found that, out of several, one alone survived (Fig. 95). But in Anaptychia ciliaris and in Lecanora subfusca Baur'' considers it proved that severalshare in the formation of theapothecium. In this connection it is interesting to note that, according to Harper' and others, several ascogonia enter into one Pyronema fruit. (4) The ascogonial cells, before and after ferti- lization, are distinguished from the surrounding hyphae by a reaction to various stains, which is dif- ferent from that of the vegetative hyphae, and also by the shortness and width of their cells. The whole of the apothecial primor- dium 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^ noted that some of the cells failed to develop. (6) The hyphae from the ascogonial cells spread out in a complex layer at the base of the hymenium, and send up branches which form the asci, either, as in most Ascomycetes
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