72 



RHODOSPERME.*;. 



duction — their position — their supposed office — tends to 

 show that they are of the nature of acrogenous leaves: — per- 

 forming such of the functions of leaves as the exigencies of 

 the plant require, some of which functions are, I admit, dis- 

 charged by the surface of the branches generally, as is the 

 case in all frondose plants, whether cryptogaraous or phaj- 

 nogaraous. No arguments, based on their imperfect deve- 

 lopment, affect their morphological relations: — and if we 

 may be allowed to regard these ramelli as the representatives 

 of leaves, we establish the first step in our argument. 



We have next to determine the morphology of the cera- 

 midium, or spore-case, in which the tuft of spores is con- 

 tained. The inspection of any PolysipJionia, Dasya, 

 RJiodomela or Laurencia is sufficient to show that, in these 

 genera, the ceraniidium is simply a truncated branch of the 

 frond : — a branch diverted fi'om its normal character and 

 changed into an ovate or pitcher-shaped, hollow body, 

 pierced at the apex and containing a tuft of spores. Let us 

 observe how this metamorphosis has occurred. The cera- 

 midiuiu makes its appearance as a young branch does, from 

 the side of an old one ; or else it is formed at the apex of 

 an old branch. In either case it is at first a little round 

 knob, destitute of apical fibres {rcunelll). This knob gradu- 

 ally swells, but does not greatly lengthen — becomes urceolate 

 or ovate — and is at last pierced at the apex. On opening it 

 we find a tuft of fibres with their terminal cells converted 

 into pear-shaped spores, attached to the cellular placenta at 



the base of the spore-case. 

 J 1 How are we to understand 



this structure ? The length- 

 ening of the branch is ar- 

 rested at a definite point, 

 and the powers of life are 

 concentrated on the elabora- 

 tion of the contents of the 

 ceramidium. The placenta 

 at the base is evidently the 

 apex of the branch ; the fi- 

 bres that carry spores are evi- 



* Explanation of Diagram. Fig. 1 .—Supposes the peripheric stratum 

 (i) to have grown beyond the true apex (a) to a certain point, forming the 

 outer membrane of the wall of the ceramidium, and then to have doubled 

 back, and returned along the inside of the wall to the insertion of the spores, 

 (f) ; forming thus a double membrane. Fig. 2.— Simply supposes the stra- 

 tum (b) to have grown beyond the ape.x (a) leaving a cavity, containing the 

 spores (c) at its base. 



Diagram of supposed Structure of 

 a Ceramidium* 



