On THE PITHOPHORACES. 37 
and h, and pl. 71 gagropila socialis)*). Organs perfectly resembling 
these, Pithophoracew have not, it is true; but a comparative study has 
convinced me that the accessorial branches sometimes developed from 
the cauloid cells of the Pithophoracew, which proceed, like the rhizines 
of the Cladophoree, 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 ofthe 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 Cladophoree connecting forms occur between real rhizines, which 
serve as attaching organs, and the basal accessorial branches of Pitho- 
phoracee; see Kiirz. |. c., pl. 82 Spongomorpha uncialis (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 Pitho- 
phoracee and Cladophoree 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 Pithophoracee however unlike it may seem 
to that of the Cladophoree — 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 Cladophorew. 
If it is, consequently, perfectly evident with which group of plants 
the Pithophoracee show the greatest conformity as to the vegetative 
system, it is very much more difficult to determine the group which 
1) 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 Kitz. 1. ¢. pl. 70 
Agagropila repens, pl. 74 Spongomorpha arcta, pl. 75 8. spincscens, pl. 76 8. rhizo- 
phora, and pl. 77—80. 
eC. eh C—O 
ae 
