368 WILLIAM ARCHER. 



occur the isolated heterocysts; the spores large, broadly 

 elliptic, about one third longer than broad ; their diameter 

 more than twice the diameter of the heterocysts, about thrice 

 the diameter of the ordinary cells ; the" " bright points " of 

 the heterocysts not very conspicuous. (See PL XXI, fig. 18.) 



I would explicitly deprecate any supposition that the obser- 

 vation was founded on any mere isolated filament, met with in 

 the same material as the rest of the ordinary examples of this 

 Nostic around, and assumed by me to have emanated from 

 some of them, and, therefore, possibly that of some other 

 genus. The filaments were not isolated, but, contorted about 

 in quite the ordinary Avay, Avere still involved in the parent 

 matrix, which was bounded by the distinct i)ellicle, or 

 " periderm," generically characteristic, and in all respects, 

 save the remarkable speciality described, this example was 

 absolutely the same as the others in the same gathering ; in 

 fact, the little Nostoc was intact. It might be said, possibly, 

 this little plant was rather a Monovmia, but the definite 

 periderm to the rounded fronds places a bar to the assump- 

 tion, and I do not think any observer would see it and 

 pronounce it other than a Nostoc. 



In making a drawing for illustration, it is of course un- 

 necessary to present more than one spore, with its adjacent 

 heterocysts and a few cells of the filament. To give the 

 total frond, and its long, tortuously looped and curved 

 filaments, with their numerous spores and heterocysts, and to 

 convey an idea of the matrix, with the bounding periderm, 

 would have been an unnecessary labour and expense, and to 

 carry it out on the scale of some 400 diameters would have 

 occupied a very considerable space. 



I would now advert to Professor Reess's views, as given in 

 his memoir above alluded to. This observer is an adherent 

 of the hypothesis already jDropounded by Professor Schwen- 

 dener, as regards the nature of Lichens, who, in his turn, 

 seems possibly to have had suggested to him the working out 

 of some such idea as he has arrived at by the alternative con- 

 clusion piit forward by Professor de Bary, as one or other 

 being a necessary outcome or result deducible from the 

 existent knoAvledge of the gelatinous Lichens (Gallertfletchen) 

 or the Collemacese and allies, and seemingly embracing also 

 Ephebe in his generalisation. This the latter thus enun- 

 ciates : — '• Either the Lichens in question are perfectly 

 developed states of plants whose imperfectly developed forms 

 have hitherto stood among the Algse as the Nostocacea3 and 

 Chroococcaceee. Or the Nostocaceae and Chroococcacese are 

 typical Algse — they assume the form of CoUema, Ephebe, and 



