Division A comprises (a) the true Ascomycetes, of which the moulds Eurotium and Penicillium are examples, and (b) the Hemiasci, which includes the yeasts.
In some of the true Ascomycetes, such as Penicillium glaucum, the conidia if grown in saccharine solutions, which they have the power of fermenting, develop single cell yeast-like forms, and do not - at any rate for a time - produce again the characteristic branching mycelium.
The Ascomycetes, Rust Fungi, &c., the same structure obtains so far as all essential details are concerned.
In 1865 De Bary suggested the possibility that such lichens as Collema, Ephebe, &c., arose as a result of the attack of parasitic Ascomycetes upon the algae, Nostoc, Chroococcus, &c. In 1867 the observations of Famintzin and Baranetzky showed that the gonidia, in certain cases, were able to live outside the lichen-thallus, and in the case of Physcia, Evernia and Cladonia were able to form zoospores.
Contrary to the behaviour of the non-lichen forming Ascomycetes the lichen-fungi show very few cases of ordinary conidial formation.
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