94 HICKSj ON GONIDIA OF LICHENS. 



at Nostoc are indicated in figs. 17, 18, 19. Comparing these 

 with the changes in CoUema-gonidia, the similarity is evi- 

 dent. At fig. 15 a is shown a perfect apothccia, where all 

 the gonidia are now fully developed Nostoc balls. 



From the evidence just brought forward, in addition to 

 that advanced by Itzigsohn and Sachs above spoken of, I con- 

 ceive Ave can no longer consider Nostoc as an alga ; but that 

 we must, in company with Gleocapsa, Pahnogloia, Sec, confide 

 them to the care of licheuologists, and thus add a new field 

 for their observations, and a ncAv phase in the life-history 

 of those curious organisms. 



Hitherto the origin of Nostoc has only been traced up to 

 Collema, and to the gymnocarpous lichen above mentioned ; 

 but as researches have only been recently made in this direc- 

 tion, it is by no means improbable that other instances may 

 be added to their number. 



There is one point to which I wish to draw the attention 

 of observers, namely, to watch the changes which the Col- 

 lema- and Nostoc-gonidia may undergo; for, from what I 

 have shown above, it surely cannot be considered an impos- 

 sibility that they may assume a great variety of conditions, 

 and thus give rise to many of the Nostochacese. Indeed, it 

 has been stated by Itzigsohn^^ as his opinion that all the 

 Nostochacepe are, in all probability, derived from the gonidia 

 of lichens. Whether this be the case, partially or wholly, 

 or not, from what has been shown at figs. 8, 9, 10, 11, such 

 a condition is possible ; for if the beaded threads of Nostoc 

 can become modified into such forms as arc represented at 9 cr, 

 the mucous coating becoming broken up at the same time, 

 setting them free, it certainly cannot be considered beyond 

 the range of physiological probability for them to develop 

 themselves into one of the linear Nostochacese ; for let us 

 suppose, instead of a short portion of a Nostoc thread be- 

 coming changed, as at figs. 10 and 11^ that a long portion 

 was so affected, or that the short portion so affected con- 

 tinued to segment linearly, and reproduce the altered state — 

 a process Avhich obtains in other vegetations — then we should 

 have forms allied to, if not identical with, the Nostochaceae. 

 Supposing such a condition proceeded intermittently, how 

 could it be recognised from such forms as TricJiormus, 

 Sphcerozyga, SjJO'/nosira, Doiichospermwn, &c. ? I am not, 

 from direct observation, prepared to assert that such is the 

 origin of these growths ; but the following fact seems to b6 

 strongly confirmative of Itzigsohn' s opinion. 



4 r 



Botan. Zeitucg,' 1854, p. 521. 



