. Lichens. Lichens. REPRODUCTION IN DISCOLICHENS i6i. the view that there had been fertilization: the cells of the trichogyne had lost their turgidity and at the same time the cross-walls had swollen con- siderably and stood out like knots in the hypha (Fig. 92). The ascogonial cells had also increased not only in size but in number by intercalary division, so that the spiral arrangement became obscured. Ascogenous hyphae arose from the ascogonial cells, and asci cut off by a basal septum were finally formed from these hyphae. Lateral branches from below the septum also formed asci. Stahl's ob
. Lichens. Lichens. REPRODUCTION IN DISCOLICHENS i6i. the view that there had been fertilization: the cells of the trichogyne had lost their turgidity and at the same time the cross-walls had swollen con- siderably and stood out like knots in the hypha (Fig. 92). The ascogonial cells had also increased not only in size but in number by intercalary division, so that the spiral arrangement became obscured. Ascogenous hyphae arose from the ascogonial cells, and asci cut off by a basal septum were finally formed from these hyphae. Lateral branches from below the septum also formed asci. Stahl's observations were repeated and extended by Borzi^ on another of the Colle- maceae, Colleina nigrescens. In that plant the foliaceous thallus is of thin texture and has a distinct cellular cortex. The carpogonia were found at varying depths near to the cor- tical region; the ascogonium, of two and a half to four spirals, consisted of ten to fifteen cells with very thin walls, the trichogyne of five to ten cells, the terminal cell projecting above the thallus. Borzi also found spermatia fused with the tip-cell. A further important contribution was made hy Baur" in his study of Collema crispum^. There occur in nature two forms of this lichen, one of them crowded with apothecia and spermogonia, the other with a more luxuriant thallus, but with few apothecia and no spermogonia. On the latter almost sterile form Baur found in spring and again in autumn immense numbers of carpogonia-—about one thousand in a medium sized thallus— which nearly all gradually lost the characteristics of reproductive organs, and, anastomising with other hyphae, became part of the vegetative system. In a few cases in which, presumably, a spermatium had fused with a tricho- gyne, very large apothecia had developed. As the first-mentioned form was always crowded with apothecia in every stage of development, as well as with carpogonia and spermogonia, it seemed natural to conclude that the difference wa
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