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.
Nostoc lichenoides in most of rutida in Omphalaria; Lichina, in Peltigera, Pannaria and Stictina; Gloeocapsa polydermatica in Baeomyces and Omphalaria; Sirosiphon pulvinatus in Ephebe pubescens.
In the case of Solorina, for example, the principal alga is a green alga, one of the Palmellaceae, but Nostoc (a blue-green alga) is also found playing a subsidiary part as FIG.
- Section of Homoiomerous Thallus of Collema conglomeratum, with Nostoc threads scattered among the hyphae.
(Cystococcus, Nag.) C, Nostoc from the thallus of Physma attacked by the germ-tube from a chalazanum.
With Nostoc or Scytonema gonidia.
Certain species are regularly found in the intercellular spaces of higher plants; such are species of Nostoc in the thallus of Anthoceros, the leaves of Azolla and the roots of Cycads.
The cells of the filament may be all alike, and growth may occur equally in all parts (Oscillatoriaceae); or certain cells (heterocysts) may become marked off by their larger size and the transparency of their contents; in which case growth may still be distributed equally throughout (Nostoc), or the filament may be attached where the heterocyst arises, and grow out at the opposite extremity into a fine hair (Rivulariaceae).
Nostoc sp., young colony-fila ment with heterocysts.
Nostoc colonies are constantly present in a special cavity of the dorsal lobe of the leaf in Azolla.