36 



Veit Brecher Wittrock. 



of the thallus is, in short, so great that it sometimes meets with no small diffi- 

 culty to identify, solely by the cauloid part, whether a sterile specimen 

 belongs to a Cladophora or to a Pitltoplwra (on the distinguishing char- 

 acters in this case, see parag. 1, pag. 4). What gives sure distinctions, 

 even if only the vegetative organs are taken into consideration, is, on 

 the contrary, the nature of the rhizo'id system. In Pithoplioracece this 

 consists, as a rule, of only one cell, viz. the one developed, immediately 

 at the germination of the hypnospore, in a direction diametrically oppo- 

 site to that of the cauloid. This rhizo'id cell (which has, as we know, 

 nothing to do with the attaching of the thallus) we regard, from reasons 

 mentioned page 5, as analogous, in some degree at least, with the tap-root 

 of the Dicotyledonece. But in Cladophorew (particularly in Cladophora fracta 

 (Dillw.) Kiitz., which in other respects belongs to the most Pithophora-Y&o, 

 species) the spore — which is here a zoospore — sends forth downwards, 

 in germinating, one or generally several irregularly formed processes, 

 serving as attaching organs, rhizines, which have nothing in common 

 with the tap-root, but show a certain analogy to the adventitious roots 

 developed in the germination of the Monocotyledonew. As no formation 

 of parting-walls takes place between these rhizines and the germinated 

 spore, they will consist merely of processes belonging to the lowest 

 one of the cauloid cells, not of independent cells. In a great many 

 Cladophorew, however, these rhizines are not the only constituent parts 

 of the rhizo'id system. *) A plentiful development of pluricellular rhizines, 

 comparable to the adventitious roots from the stem of the higher plants, 

 takes place in the cauloid, especially in the genera of JEgagropUa Kiitz. 

 and Spongomorplta Kiitz. These rhizo'id organs are recognized as such 

 by the circumstance that they are developed, in contrast to the cauloid 

 branches, from the lowest part of their mother cells; that they increase 

 downwards; that they contain but little chlorophyll; and that they serve 

 as real attaching organs, which rather often have the end of the lowest 

 cell transformed into a peculiar grasping organ, sometimes resembling a 

 helicoid (see KtiTZ. Tab. Phyc, part 4, pi. 83 Spongomorpha lanosa fig. g 



pestina which 'gives reason to suppose that helicoids of the same nature occur also in 

 this form of JEgagropda. Besides these unicellular attaching organs, perfectly resem- 

 bling those of the Pithopliora-helico'i&s, pluricellular helicoids with a top rolled like 

 a spiral or bent like a claw are found in numerous Cladoplwrece belonging to the 

 genus Spongomorpha Kiitz.; see Kutz. 1. c, pi. 75 — 78. 



J ) I am not quite certain whether all Cladophoreos have other rhizines be- 

 sides those developed from the germinated spore. 



