Aquatic Botany, 10 (1981) 161--173 161 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands TURION FORMATION, DORMANCY AND GERMINATION OF CURLY PONDW~ED, POTAMOGETON CRISPUS L. SOETIKNO S. SASTROUTOMO Biological Institute, Faculty of Science, Tohoku University, Aramaki-Aoba, Sendal 980 (Japan) (Accepted 23 October 1980) ABSTRACT Sastroutomo, S.S., 1981. Turion formation, dormancy and germination of curly pond- weed, Potamogeton crispus L. Aquat. Bot., 10: 161--173. Turion formation, dormancy, and germination in curly pondweed (Potamogeton crispus L.) was investigated under natural condition as well as in growth chambers. In Lake Oja- gaike, Chiba, turions started to germinate and develop in late autumn, reaching maximum development during May. Flowering took place in late spring (May) and fruits could be collected during May--June. Turions were formed during May-June, turion development taking about two weeks. Non-dormant turions collected from the lake were of two different colours, brown and green. The rate of germination of brown turions was lower than that of green turions. The germination of non-dormant green turions was affected by water temperature but not by light intensity. Dormancy was fully broken by a cold treatment (5°C) for 1 week, a warm treatment (30°C) for two weeks or a heat treatment (35 ° C) for two weeks, but not by an almost freezing temperature (--1 to 2° C). There was significant interaction between the length of heat treatment and light or dark conditions. IAA and GA 3 (10 -5 and 10 -6 M) broke dormancy of warm-treated turions, however in high con- centrations (10 -3 and 10 -4 M) the dormancy was fully broken even in non warm-treated turions. With higher concentrations GA 3 promoted shoot elongation in light, whereas in the dark, shoot elongation was inhibited. INTRODUCTION The importance of the aquatic environment is becoming more evident with the present concern for ecology. Many aquatic plants have been shown to be indicators of water quality and of changes in the aquati( environment. Certain species, e.g. Najas flexilis (Willd.) Rost. & Schmidt, Potamogeton amplifolius Tuckerm., P. friesii Ruprecht and P. strictifolius A. Benn. are in- tolerant to polluted waters, while other species, e.g. Najas minor All., Pota- mogeton foliosus Raf., P. pusillus L., and Vallisneria americana Michaux, are tolerant (Lind and Cottam, 1969; Seddon, 1972). Potamogeton crispus L., one of 16 species of Potamogeton found in Japan is successfully colonising the freshwaters of the country and is considered to 0304-3770/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company