. Lichens. Lichens. 92 MORPHOLOGY retain the colour of the cortex and are greyish or whitish-grey, as in Physcia ciliaris or in Physcia hispida (Fig. i lo). They provide a yellow fringe to the apothecia of Physcia chrysophthalma and a green fringe to those of Usnea florida. They are dark-brown or almost black in Parmelia perlata var. ciliata and in P. cetrata, etc. as also in Gyrophora cylindrica. The fronds of Cetraria i^landica and other species of the genus are bordered with short spinulose brown hairs whose main function seems to be the bearing of "pycnidia" though in many cases
. Lichens. Lichens. 92 MORPHOLOGY retain the colour of the cortex and are greyish or whitish-grey, as in Physcia ciliaris or in Physcia hispida (Fig. i lo). They provide a yellow fringe to the apothecia of Physcia chrysophthalma and a green fringe to those of Usnea florida. They are dark-brown or almost black in Parmelia perlata var. ciliata and in P. cetrata, etc. as also in Gyrophora cylindrica. The fronds of Cetraria i^landica and other species of the genus are bordered with short spinulose brown hairs whose main function seems to be the bearing of "pycnidia" though in many cases they are barren (Fig. 128). Superficial cilia are more rarely formed than marginal ones, but they are characteristic of one not uncommon British species, Parmelia proboscidea { Hue). Scattered over the surface of that lichen are numerous crowded groups of isidia which, frequently, are prolonged upwards as dark- brown or blackish cilia. Nearly every isidium bears a small brown spot on the apex at an early stage of growth. Similar cilia are sparsely scattered over the thallus, but their base is always a rather stouter grey structure, which suggests an isidial origin. Cilia also occur on the margin of the lobes. As lichens are a favourite food of snails, insects, etc., it is considered that these structures are protective in function, and that they impede, if they do not entirely prevent, the larger marauders in their work of destruction. b. Rhizinae. Lichen rootlets are mainly for the purpose of attachment and have little significance as organs of absorption. They have been noted in only one crustaceous lichen, Varicellaria microsticta^, an alpine species that spreads over bark or soil, and which is further distinguished by being. 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 perfectly resemble the original Smith, Annie Lorrain.
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Keywords: ., bookcentury1900, bookdecade1920, bookpublishercambr, bookyear1921
