Lindau[563] published results of the examination of a considerable series of lichens. In Anaptychia (Physcia) ciliaris, Physcia stellaris, Ph. pulverulenta, Ramalina fraxinea, Placodium (Lecanora) saxicolum, Lecanora subfusca and Lecidea enteroleuca he demonstrated the presence of ascogonia with trichogynes. In Parmelia tiliacea and in Xanthoria parietina he found ascogonia but failed to see trichogynes. In none of the species examined by him did he observe any fusion between the trichogyne and a spermatium.
In Anaptychia ciliaris he was able to pick out extremely early stages by staining with a solution of chlor-zinc-iodine. Mäule[564] applied the same test to Physcia pulverulenta, but found that to be successful the reaction required some time. Certain cells of the hyphae—mostly terminal cells—in the lower area of the gonidial zone and even occasionally in the pith (according to Lindau) coloured a deep brown, while the ordinary thalline hyphae were tinted yellow. He assumed that these were initial ascogonial cells on account of the richer plasma contents, and also because of the somewhat larger size of the cells. In the same region of the thallus young carpogonia were observed as outgrowths from vegetative hyphae, though the trichogynes had not yet reached the surface.
Fig. 93. Physcia pulverulenta Nyl. Vertical section of thallus and carpogonium before fertilization. a, outer cortex; b, inner cortex; c, gonidial layer; d, medulla. × ca. 540 (after Darbishire).
Fig. 94. Physcia (Anaptychia) ciliaris DC. Vertical section of developing ascogonium. a, paraphyses; b, ascogonial hyphae; c, ascogonial cells. × 800 (after Baur).
At a more advanced stage the carpogonia were seen to be embedded in the gonidial zone and occurred in groups. The cells of the ascogonium, easily recognized by the darker stain, were short and stout, measuring about 6-8µ in length and 4·4µ in width. They were arranged in somewhat indistinct spirals; but the crowding of the groups resulted in a confused intermingling of the various generative filaments. The trichogynes composed of longer narrower cells rose above the hyphae of the cortex; they also stained a deep brown and the projecting cell was always thin-walled. Lindau frequently observed spermatia very firmly attached to the trichogyne cell but without any plasma connection between the two. The changes in the trichogyne described by Stahl and Baur in Collemaceae were not seen in Anaptychia; the peculiar swelling of the septa seems to be a phenomenon confined to gelatinous lichens. During the trichogyne stage in this lichen the vegetative hyphae from the medulla grow up and surround the young carpogonia, and, at the same time, very slender hyphae begin to branch upwards to form the paraphyses. Darbishire’s[565] examination of Physcia pulverulenta demonstrated the presence of the coiled ascogonium and the trichogyne in that species ([Fig. 93]).
Baur[566] has also given the results of an examination of Anaptychia. He frequently observed copulation between the spermatium and the tip of the trichogyne, but not any passage of nucleus or contents. After copulation the ascogonial cells increased in size and became irregular in form, and open communication was established between them ([Fig. 94]). There was no increase in their number by intercalary division as in Collema. After producing ascogenous hyphae the cells were seen to have lost their contents and then to have gradually disappeared. The fertile hyphae, which now took a blue colouration with chlor-zinc-iodine, gradually spread out and formed a wide-stretching hymenium. Several carpogonia took part in the formation of one apothecium.
The tissue below the ascogonium meanwhile developed vigorously, forming a weft of encircling hyphae, while the upper branches grew vertically towards 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.