On the Pithophoeace^. 37 



and A, and pi. 71 JEgagropila socialis) ^). Organs perfectly resembling 

 these, Pithophoracece have not, it is true; but a comparative study has 

 convinced me that the accessorial branches sometimes developed from 

 the cauloïd cells of the Pithophoracece^ which proceed, like the rhizines 

 of the Cladophoreœ^ from the lowest part of their mother cells, and take, 

 like these, their increase downwards (see parag. 3, page 27), are to 

 be regarded as the morphological equivalent of these organs, even if 

 they are not analogous to them in a physiological point of view. We 

 know that they have nothing to do with the attaching; and together 

 with the loss of their original function they have — in the same manner 

 as the principal rhizoïd of the thallus — also lost the shape of attaching 

 organs (rhizine branches) and assumed instead the shape of common 

 cauloïd branches. They would thus require to be regarded as regres- 

 sively transformed rhizines, or as a kind of rhizine rudiments. What 

 gives increased probability to this vieAv of their character is, that in 

 some Cladophoreœ connecting forms occur between real rhizines, which 

 serve as attaching organs, and the basal accessorial branches of Pitho- 

 plioracece; see KüTZ. 1. c, pi. 82 Spongomorpha uncialis (baltica) figs, a 

 and h. 



We may perceive from the comparison made above, that the only 

 essential difference which exists between the vegetative system of Pitho- 

 Ijhoraceœ and Cladopho7'eœ lies in the nature of the rhizoïd organs formed 

 immediately at the germination of the spore, a difference which is very 

 closely connected with the different nature of the rejDroductive organs 

 (resp. hypnospores and zoospores) of these plants. The great confor- 

 mity in everything else speaks forcibly, I think, to the advantage of a 

 close affinity between the two groups now mentioned, the more because 

 the reproductive system of Pithojjhoraceœ — however unlike it may seem 

 to that of the Cladop)horeœ — is, nevertheless, of a nature whose origin 

 may gain its explanatian (as we will endeavour to make evident here- 

 after) from certain phenomena apparent in Cladophoreœ. 



If it is, consequently, perfectly evident with which group of plants 

 the Pithophoracece show the greatest conformity as to the vegetative 

 system, it is very much more difficult to determine the group which 



^) The rhizine branches differ from the cauloïd branches also by greater length 

 and at the same time by a much smaller diameter of their cells; see KfJTZ. 1. c. pi. 70 

 JEgagropila repens, pi. 74 Spongomorpha arcta, pi. 75 S. spineaccns, pi. 76 S. rhizo- 

 phora, and pi. 77—80. 



