HICKS^ ON GONIDIA OP LICHENS. 95 



At fig. 20 I liave figured a Nostoc ball, in tlie interior of 

 which is a long, bluish-green, articulated thread {a), -which 

 has its origin in a vesicular cell (heterocyst) b ; as do many of 

 the ordinary beaded threads of Nostoc. The whole was unmis- 

 takeably ivithin the mass, and dipped towards the centre, 

 and evidently could not have been derived from without. 

 Besides, it is worthy of notice, that Nostoc balls are always 

 remarkably free from extraneous matter ; a condition to be 

 explained by their mode of increase. Hence we may con- 

 clude that this growth had its origin from the Nostoc- 

 gonidia. 



There is another fact which may perhaps help us, 

 namely, that in contact with some Nostoc balls are to be 

 found many forms of these linear Nostochaceae ; they are so 

 intimately united, and so mixed up Avith them, as must to 

 any observer be suggestive of an intimate connection. Such 

 forms I have represented at figs. 21 and 22 -, and if we admit 

 the articulated thread at fig. 20 to have had a Nostoc origin, 

 then there is no difficulty in accepting a similar source for 

 those at figs. 21 and 22 — a form allied to Schhosqjiion. In 

 the same position I have seen Scytonema. 



For these observations I do not wish to claim more import- 

 ance than they deserve ; still they bear strongly upon the 

 opinion advanced by the author above named. 



In the papers of Itzigsohn"^ on the diamorphosis of 

 C'hroococciis and Gleocapsa, and on the relation of Nostoc and 

 the Nostochaceae to Collema, there are many remarks which, 

 although they may not be immediately assented to by English 

 observers, yet are worthy, to say the least, of careful con- 

 sideration ; and as he is in part supported by Kiitzing, and 

 by some observations of \. Flotow on the Eijhebe pubescens, 

 many points which he has advanced should scarcely be passed 

 aside, without good negative evidence, with such remarks as 

 these, " We do not place much reliance on the statements of 

 Itzigsohn.^^t To enter into the whole question of the rela- 

 tions of Lyngbya, Ulothrix, &c., is not within the inten- 

 tion of the present contributions ; but, the possibility being- 

 granted upon ordinary physiological grounds, we should be 

 prepared to put aside our former notions upon any well- 

 proved fact appearing. Besides, there is nothing difiicult in 

 supposing that some forms of Pahnella cruenta, for instance, 

 represent the unicellar condition of some of the Oscillatoria?, 

 which have broken up into single cells; and then that these latter 



» 'Bot. Zeitung/ 1854, pp. 520 and 642. 

 t « Micrograph. Diction.,' 2d edit., p. 496. 



