4. Veit Brecuer Wrrrrock. 
I. CONSTRUCTION OF THE VEGETATIVE SYSTEM. 
The Pithophoracee belong to those simply constructed plants, 
whose vegetative system consists of a thallus, formed only of ramified 
series of cells. In a sterile condition (pl. 1, fig. 7 and 8) they resemble 
the common freshwater Cladophoree so much, that it seems at first im- 
possible to distinguish them from each other in this condition. By a 
nearer examination, however, you succeed in finding two characters by 
the assistance of which it is possible to distinguish even sterile Pitho- 
phoracee from Cladophoree. One of these characters is, that in Pitho- 
phoracew the branches are, as a rule, attached to their supporting cells a 
small space below their top; a space in general of the same or not much 
less length than the diameter of the branch cells. The other character is, 
that the vegetative cells in Pithophoracew are, it is true, rather long, 
but that the length is however very variable (5—12—20 times longer 
than the thickness, and still more), not only in the same species, but 
in the same individuals. Of all the numerous species of real Cladophoree 
which I have had occasion to examine or of which I have seen trust- 
worthy figures, there are only two, that have regularly their branches 
attached to the supporting cells in the same manner as Pithophoracee. 
These two are Cladophora uncialis Fl. Dan. *), (which occurs in the salt 
water on the coasts of the North Sea and Cattegat), and Cladophora 
tomentosa Sur., (found on moist earth in Japan). ”) These species do 
not, however, make the same impression as a Pithophora, their vegeta- 
tive cells being proportionally short (only 2—4 times: as long as thick), 
and, moreover, they are all of about the same length. 
If you observe the whole thallus of a complete specimen for in- 
stance of Pithophora kewensis nob. (pl. 2, fig. 1, 5, 6 and 7) you will 
find, that it consists of two very easily distinguished parts, situated one 
1) It is Professor J. HE. Arescnovue who has indicated to me, that the branches 
of Cl. uncialis Fl. Dan, are attached in this peculiar manner. 
2) In Cladophora comosa Kiitz. and Cl. Kjellmanniana Wittr. (a new spe- 
cies from the glaciers of Spitzbergen) it sometimes happens, it is true, that part 
of the branches are attached in the same manner as in the Pithophoraceeé; but this 
mode of attachment is not the regular one. In the groups Rhizoclonium Kiitz. and 
Zligagropila Kiitz. the attaching point of the branches, especially of the lower ones, 
is very irregular, and with those it now and then happens, that one or two branches 
have the same position on their supporting cell, as that which the Pithophoracee 
regularly have, 
a i. 
