331 



or pitcher-shaped hollow body, pierced at the apex, and con- 

 taining a tuft of spores. That a ceramidium is really a meta- 

 morphosed branch is apparent from the inspection of any plant 

 of the family; no phycologist will deny the assertion, so I shall 

 not waste the Academy's time by proving it, but proceed to 

 inquire what metamorphosis has taken place. 



"The ceramidium makes its appearance, as a young branch 

 does, on the side of an old one ; or it is formed but rarely at 

 the apex of the branch. In either case it is at first a little 

 round knob, destitute of apical fibres. This knob gradually 

 swells, but does not greatly lengthen, becomes urceolate or 

 ovate, and is finally pierced at the apex. On opening it we 

 find a tuft of fibres, with their terminal cells converted into 

 pear-shaped spores, attached to a cellular placenta at the base 

 of the spore-case. What metamorphosis have we here? The 

 lengthening of the branch is stopped, and the powers of life 

 concentrated on the elaboration of the contents of the cerami- 

 dium. The placenta at the base of the ceramidium is evidently 

 the proper apex of the branch ; if this be so, the walls of the 

 ceramidium, as well as the stalked spores within, are probably 

 transformations of the apical fibres. Or we may suppose an 

 introversion of the apex to take place, analogous to what ap- 

 pears to occur in the Fuci ; or that, the onward growth of the 

 branch being stopped, owing to the altered condition of the 

 apical fibres (the cause of this altered condition being a fertili- 

 zation of their cells), the cellular substance continues to deve- 

 lope laterally for a time, until it have formed the walls of the 

 conceptacle. Whichever hypothesis we adopt, I think we are 

 warranted in regarding the tuft of spores as the metamorphosed 

 apical fibres. 



" I have already endeavoured to show the probability that 

 the apical fibres are the analogues of leaves. If this be admit- 

 ted, and that it be also admitted that the contents of the cera- 

 midium are apical fibres diverted to another purpose, then we 

 shall have strong analogical evidence in favour of the seminal 



VOL. IV. 2 c 



