Contributions to the Knowledge of the Development of the Gonidia of Lichens, in Relation to the Unicellular Algæ, &c

ABSTRACT Before entering upon the subject I have proposed for consideration in the present contribution, it will be needful to remark that, in 1854, H.Itzigsohn,inthe ‘Botanische Zeitung’ (“Wie verhält sich Collema zu Nostoc und zu Nostochineen)” page 521, and J. Sachs, in the same journal, in 1855, 5th January (“Zur Entwicklungsgeschichte des Collema, &c.”), insisted upon the origin of Nostoc from Collema; and they have pointed out one method by which Nostoc springs from that Lichen; namely, from a small ball of the jelly-like mucus, enclosing a few of the beaded cells, which becomes extruded from the parent thallus. When one such ball becomes free, it may take one of two modes of development: 1st, it may produce the continuous colourless threads, and thus pass into Collema (fig. 7); or 2nd, without any tendency to the formation of these fibres, the ball will increase in size and transparency, become less dense, while the green beaded filaments increase by subdivision, and the heterocysts common to the Nostochaceæ are found at intervals. This latter is Nostoc, and this is one method by which it may arise. In the same condition the development may continue for an indefinite period. The first stages are shown at Pl. V, figs. 5 and 6.