. Lichens. Lichens. 32 CONSTITUENTS OF THE LICHEN THALLUS parasitic condition. He proposed the happily descriptive designation of a Symbiosis or conjoint life which was mostly though not always, nor in equal degree, beneficial to each of the partners or symbionts. b. Different Forms of Association. The type of association be- tween the two symbionts varies in different lichens. Bornet', in describing the development of the thallus in certain members of the Collemiaceae, found that though as a rule the two elements of the thallus, as in some species of Collema itself, persisted intact side by s
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. Lichens. Lichens. 32 CONSTITUENTS OF THE LICHEN THALLUS parasitic condition. He proposed the happily descriptive designation of a Symbiosis or conjoint life which was mostly though not always, nor in equal degree, beneficial to each of the partners or symbionts. b. Different Forms of Association. The type of association be- tween the two symbionts varies in different lichens. Bornet', in describing the development of the thallus in certain members of the Collemiaceae, found that though as a rule the two elements of the thallus, as in some species of Collema itself, persisted intact side by side, there was in other members of the genus an occasional parasitism: short branches from the main hyphae applied themselves by their tips to some cell of the Nostoc chain (Fig. 9).- The cell thus seized upon began to increase in size, and the. Fig. g. Physma chalazanum Arn. Cells of Nostoc chains penetrated and enlarged by hyphae x 950 (after Bornet). plasma became granular and gathered at the side furthest away from the point of attachment. Finally the contents were used up, and nothing was left but an empty membrane adhering to the fungus hypha.. In another species the hypha penetrated the cell. These instances of parasitism are most readily seen towards the edge of the thallus where growth is more active; towards the centre the attached cells have become absorbed, and only the shortened broken chains attest their disappearance. The other cells of the chains remain uninjured. In Synalissa, a small shrubby gelatinous genus, the hypha, as described by Bornet and by Hedlund^ pierces the outer wall of the gelatinous alga {Gloeocapsa) and swells inside to a somewhat globose haustorium which rests in a depression of the plasma (Fig. lo). The alga, though evidently ^ Bornet 1873. ' Hedlund 1892.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfe