The thallus of Stictaceae has been regarded by Nylander[424] and others as one of the most highly organized, not only on account of the size attained by the spreading lobes, but also because in that family are chiefly found those very definite cup-like structures which were named “cyphellae” by Acharius[425]. They are small hollow depressions about 1/2 mm. or more in width scattered irregularly over the under surface of the thallus.
a. Historical. Cyphellae were first pointed out by the Swiss botanist, Haller[426]. In his description of a lichen referable to Sticta fuliginosa he describes certain white circular depressions “to be found among the short brown hairs of the under surface.” At a later date Schreber[427] made these “white excavated points” the leading character of his lichen genus Sticta.
In urceolate or proper cyphellae, the base of the depression rests on the medulla; the margin is formed from the ruptured cortex and projects slightly inwards over the edge of the cup. Contrasted with these are the pseudocyphellae, somewhat roundish openings of a simpler structure which replace the others in many of the species. They have no definite margin; the internal hyphae have forced their way to the exterior and form a protruding tuft slightly above the surface. Meyer[428] reckoned them all among soredia; but he distinguished between those in which the medullary hyphae became conglutinated to form a margin (true cyphellae) and those in which there was a granular outburst of filaments (pseudocyphellae). He also included a third type, represented in Lobaria pulmonaria on the under surface of which there are numerous non-corticate, angular patches where the pith is laid bare ([Fig. 72]). Delise[429], writing about the same time on the Sticteae, gives due attention to their occurrence, classifying the various species of Sticta as cyphellate or non-cyphellate.
Acharius had limited the name “cyphella” to the hollow urceolate bodies that had a well-defined margin. Nylander[430] at first included under that term both types of structure, but later[431] he classified the pulverulent “soredia-like” forms in another group, the pseudocyphellae. As a rule they bear no relation to soredia, and algae are rarely associated with the protruding filaments. Schwendener[432], and later Wainio[433], in describing Sticta aurata from Brazil, state, as exceptional, that the citrine-yellow pseudocyphellae of that species are sparingly sorediate.
Fig. 72. Lobaria pulmonaria Hoffm. Showing pitted surface. a, under surface. Reduced (S. H., Photo.).
Fig. 73. Sticta damaecornis Nyl. Transverse section of thallus with cyphella × 100.
b. Development of Cyphellae. The cortex of both surfaces in the thallus of Sticta is a several-layered plectenchyma of thick-walled closely packed cells, the outer layer growing out into hairs on the under surface of most of the species. Where either cyphellae or pseudocyphellae occur, a more or less open channel is formed between the exterior and the internal tissues of the lichen. In the case of the cyphellae, the medullary hyphae which line the cup are divided into short roundish cells with comparatively thin walls ([Fig. 73]). They form a tissue sharply differentiated from the loose hyphae that occupy the medulla. The rounded cells tend to lie in vertical rows, though the arrangement in fully formed cyphellae is generally somewhat irregular. The terminal empty cells are loosely attached and as they are eventually abstricted and strewn over the inside of the cup they give to it the characteristic white powdery appearance.