. Lichens. Lichens. Fig. 1. Physcia aipolia 'Hyh Vertical section of thallus. i/, cortex; ^, algal layer; c; medulla; d, lower cortex. X 100 (partly diagrammatic). Fig. 3. Collema nigrescens Ac\i. Vertical section of thallus. a, chains of the alga Nostoc; b-, fungal filaments, x 600. - remain distinct. The green zone can be easily demonstrated in any of the larger lichens by scaling off the outer surface cells, or by making a vertical section through the thallus. The colourless cells penetrate to some extent among the green cells; they also form the whole of the cortical and medullary tissues.
. Lichens. Lichens. Fig. 1. Physcia aipolia 'Hyh Vertical section of thallus. i/, cortex; ^, algal layer; c; medulla; d, lower cortex. X 100 (partly diagrammatic). Fig. 3. Collema nigrescens Ac\i. Vertical section of thallus. a, chains of the alga Nostoc; b-, fungal filaments, x 600. - remain distinct. The green zone can be easily demonstrated in any of the larger lichens by scaling off the outer surface cells, or by making a vertical section through the thallus. The colourless cells penetrate to some extent among the green cells; they also form the whole of the cortical and medullary tissues. These two different elements we now know to consist of two distinct organisms, a fungus and an alga. The green algal cells were at one time considered to be reproductive bodies, and were called "gonidia,'' a term still in use though its significance has 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. Cambridge, At the University Press
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