Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 63. (Budapest 1971)

Gönczöl, J.: Aquatic Hyphomycetes from the Mts. Börzsöny

of probability the actual proportions of occurrence, the changes of frequency during the year, and the distribution along the given reaches of the stream. Nevertheless, the very simplicity of the method, as well as the circumstance that the examined foam is a natural site of aggregation of the conidia and needs no artificial interference prior to and during the investigation, instigate to exploit these conditions, given by nature in the investigation of the aquatic Hyphomycetes. I collected most of my samples in one of the "inlets" of the brook, at Sample site I, where the stream describes 6 — 8 deep S-shaped curves along a reach of 400 — 500 m. The width of the brook is about 3 — 4 m. here, its depth fluctuating between 1 m. to a few cm. according to the rocky bottom. During the spring flood, the rushing water, striking against the wall of the sudden curve, excavates some considerable hollows wherein the rapid stream slackens down and eventually forms a small swirling whirlpool. If in a place like this a fallen tree or any sort of detritus obstructs the washing away of the foam—the water flowing on but the froth, as it were, filtered out—then masses of it, occasionally of great amount (10 — 15 1.), may pile up behind the obstruction. In winter and cold weather—when aerial temperature is below 0 °C —especially favourable conditions evolve for the accumulation of foam. At such times, a brook is largely covered by ice, with an ice-free zone remaining open only in the midline of the current. The heaped up floe forms an effective natural dam and prevents the scattering or sweeping away of the piles of foam. On some occasions I even found hard, frozen, crisp froth—when thawed, it released intact conidia, as whole as those present in foam of the normal consistency. I also attempted to accumulate by artificial means the spores floating in water. In order to study the conidium-filtering ability of the foam, I tried to produce bits of froth experimentally. At different points of the brook, I spilled some ml. of a detergent substance (from any of the commercial synthetics) into the stream, where upon piles of froth had soon formed and stuck on the lower portions of the bank. In these, I found less spores than in the ones evolved in the natural way, but still Fig. 1. Survey map of the research area