FIELD AND GREENHOUSE INVESTIGATIONS ON WINTER BUD PRODUCTION BY POTAMOGETON-GRAMINEUS L

Potamogeton gramineus L. winter buds were present in the Byrnes Canal in northern California from August through October. Density (number m- 2) of winter buds increased during this period and was inversely relat ed to photoperiod. Density varied from year to year (1985-1991) and ma ximum average density of 761 m-2 was recorded in 1986. In greenhouse e xperiments, winter buds were present on plants after 8-10 weeks of gro wth at a 10 h photoperiod, but not at a 14 h photoperiod. Plants grown at a 10 h photoperiod but with the dark period interrupted with eithe r 20 or 60 min of dim light at 13 muM m-2 s-1 did not produce winter b uds. Similar plants grown at a 10 h photoperiod with no interruption o f the dark period produced winter buds. Plants grown with interruption of the dark period displayed dry matter allocation patterns similar t o plants grown at a 16 h photoperiod. This information confirms earlie r reports with other species about the importance of photoperiod for i nitiating vegetative propagule formation, and will improve capabilitie s for predicting vegetative reproduction by rooted aquatic plants.