Veit Brecher Wittrock. 



I. CONSTRUCTION OF THE VEGETATIVE SYSTEM. 



The Pithophoraceœ belong to those simply constructed plants, 

 whose vegetative system consists of a thallus, formed only of ramified 

 series of cells. In a sterile condition (pi. 1, fig. 7 and 8) they resemble 

 the common freshwater Cladophoreœ 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- 

 2jhoraceœ from Cladophoreœ. One of these characters is, that in Pitho- 

 phoraceœ 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 Pithoj^horaceœ are, it is true, rather long, 

 but that the length is however very variable ('S — 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 Cladophoreœ 

 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 Pithophoraceœ. 

 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 keivensis nob. (pi. 2, fig. 1, 5, 6 and 7) you will 

 find, that it consists of two very easily distinguished parts, situated one 



^) It is Professor J. E. AeeschoüG who has indicated to mc, that the branches 

 of CJ. uncialis Fl. Dan, are attached in this peculiar manner. 



-) In Cladophora comosa Kütz. and CI. KjeUmanniana 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 Pitlioplioraceœ; but this 

 mode of attachment is not the regular one. In the groups BJiizocJonium Kütz. and 

 ^yaciropila Kütz, 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 Fitlwphoracece 

 regularly have. 



