Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 66. (Budapest 1974)

Hajdu, L.: Filamentous Algae in Városligeti-tó, Budapest

On the basis of HORTOBÁGYI'S algal catalogue (the state in November, 1973) this species is new in the Hungarian Flora. 2. Oedogonium tyrolicum WITTEOCK. — Monoecious, in the filament the oogonia are formed in ones. They are oval, with an oval aperture on their upper parts. The oospores are round-elliptical, smooth-walled and do not fill the oogonium completely. The antheridium is a little narrower than the filament. The apical cell is bluntly rounded. The vegetative cells measure 75—113 by 14—25 ^m, the oogonium is 48—53 pva wide and 73—104 pm long (MROZINSKA

—WEBB 1969: 57—10 pm in length). The oospores are 45—52 pm wide, 52—

10pm long (MROZLNSKA

—WEBB 1. c: 40—

47itm long). With the exception of the two data for length nearly all taxonomic features well fit in with the specimens found (Figs. 6—8). The species lived attached to the leaves of Najas minor. On the basis of HORTOBÁGYI'S algal catalogue this species is new in the Hungarian Flora. 3. Aphanochaete repens A BRAUN — It was found to grow as an epiphyton on Oedogonium filaments. The 10 pm long and 7 pm wide cells formed straight on occasion ramifying threads. On each cell a hair measuring up to 60 pm originates which is onion-like thickened at its base. 4. Cladophora, glomerata (L.) KÜTZ. — The bulk of the algal mat on the bottom of the pond was formed by this species. The apical cell is 45—60 ^um thick. The colony is of acropetal organization (Fig 4). In culture it developed holdfasts as illustrated in Fig. 5. There were numerous epiphytes, chiefly diatoms on the filaments. 5. Hydrodictyon reticulatum (L.)LAGERH. (= H. utriculatum ROTH and H. tenellum ROTH) — This alga of peculiar construction is abundant in eutrophic waters (KOL 1956, SÖRENSEN 1950). Ecological data The Városligeti-tó of Budapest is a temporary water. It is filled with tap water yearly once from the watersystem and has neither out- or inflow. One third of the bottom of the pond is covered with concrete, and from its other parts the sludge is reved by dredging. In 1973 subsequent to dredging the pond was filled only later, on March 30. By the time summer set in a thick algal web had developed on the bottom of the pond, which consisted of the following three layers. Lowest down were Hydrodictyon colonies embedded into a half-anaerobic deposit smelling of hydrogen sulphide. This was covered by a thick, loose, coarse-textured Cladophora mat. The algal mat was not of equal thickness everywhere and there were furrows to some depth on its surface. The bright-green Spirogyra tufts were carried into this furrows and by climbing on one another formed relatively massive conical heaps. On August 10 the amount of algae found on a quadrate meter surface of the bottom amounted to 1,8 kg fresh-weight resp. 0,48 kg dry weight in the average of three samples. Although in the pond Spirogyra was freuqent in the vegetative form, in the conjugating form it was only seldom observed. The majority of them does not reach the stage of zygospore formation. I examined a 2 m

2 spot covered with Spirogyra in a medium advanced stage of conjugation for three weeks and found the process to have progressed only in the case of a few filaments and not even $ then were spores produced. According to my observations proliferation occurs first of all in places near to the water surface. This is evidenced also by the fact that spore-formation is more frequent in case the water level of the pond decreases-