On the Pithophoracece. 



37 



and A, and pi. 71 ^Egagropila socialis) v ). 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 cauloid cells of the Pithophoracece, which proceed, like the rhizines 

 of the Cladophorece, 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 rhizoid of the thallus — also lost the shape of attaching 

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

 cauloid 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 view of their character is, that in 

 some Cladophorece connecting forms occur between real rhizines, which 

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

 plioracece; see KiiTZ. 1. c, pi. 82 Spongomorpha uncjal/s (baltica) figs, a 

 and b. 



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

 essential difference which exists between the vegetative system of Pitlw- 

 phoracece and Cladophorece lies in the nature of the rhizoid organs formed 

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

 closely connected with the different nature of the reproductive 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 Pithophoracece — however unlike it may seem 

 to that of the Cladophorece — is, nevertheless, of a nature whose origin 

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

 after) from certain phenomena apparent in Cladophorece. 



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 cauloid branches also by greater length 

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

 JEgagropila repens, pi. 74 Spongomorpha arcta, pi. 75 S. spinescens, pi. 76 S. rhino- 

 phora, and pi. 77 — 80. 



