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Hydrilla verticillata (L. f.) Royle tubers from monoecious plants andPotamogeton gramineus L. winter buds were sprouted and allowed to grow in the dark for 120 days. We measured plant length and counted the number of leaves at 2–3 day intervals.Hydrilla grew most rapidly during the first 16–17 days andPotamogeton grew most rapidly during the first 16–25 days. Measurement of propagule carbon content over time indicated that cessation of rapid growth coincided with depletion of tuber carbon by one-half forHydrilla. ForPotamogeton, growth was reduced after 16 to 25 days while the winter bud C half-life was 37 days. Calculations indicated thatHydrilla mobilized 49% andPotamogeton 39% of the initial propagule carbon to support growth. In a second experiment, in which plants were grown in substrate the plants grew taller and produced slightly more leaves per plant.Potamogeton removed from darkness after specified time periods, and allowed to grow for 21 days in a greenhouse recovered from 20–30 days in the dark. Similarly treatedHydrilla plants recovered from up to 80 days in the dark.Potamogeton had mobilized 79% of initial C by the time it was unable to recover from the dark treatment. Combined results for both species indicate that the majority of propagule C was utilized in the first 16 to 30 days following sprouting. In conjunction with an understanding propagule sprouting requirements, this information will be useful in the timing of application for management techniques.

Hydrilla verticillata (L.f.) Royle produces two types of vegetative propagules, subterranean turions and axillary turions. After 8 or 12 weeks growth under similar conditions, plants grown from subterranean turions weighed 1.7 to 2 times as much as plants grown from axillary turions. Subterranean turion-derived plants produced more propagules (by weight and number) per plant than plants from axillary turions. Characteristics of weight frequency distributions (median, minimum, maximum, and coefficient of variation) for new subterranean turions were also influenced by the type of propagule from which the parent plant was derived. The number of root crowns per plant which reflects the plant's ability to expand horizontally was significantly greater for subterranean turion-derived plants (by 2 times) than for plants from axillary turions. These results support the hypothesis that following colonization of an area the impact ofHydrilla on resident species changes over time.

The zooplankton community in Lake Charles East, Indiana, was sampled from June, 1974 through September, 1977 as part of a lake restoration study. About 1.8 × 104 kg of lime and 1.8 × 106 kg of ponded fly ash were added to the lake during May through August, 1975 to precipitate phosphate and seal the sediments. Annual mean species number (5.2–11.3) and annual mean species diversity (H′, 0.9–1.3) were highest in 1976, the first year after treatment. By the second post-treatment year these variables had returned to pretreatment levels. Prior to treatment Cladocera were dominant during fall and early winter (Sept.–Dec. 1974), with Copepoda dominant in late winter and spring (Jan.–May 1975). After treatment Cladocera were dominant throughout the fall and winter (Nov. 1957–May 1976). Copepoda were again dominant in August 1976. The short term effect of the treatment appeared to be termination of the latter part of the copepod annual cycle through elimination of aestivating copepodites in the summer and increased abundance of Cladocera during the winter and spring immediately following treatment. Community composition one year after treatment was similar to that observed prior to treatment.