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A Thermogradient Incubator for Seed Germination Studies¹

Multiple temperature regimes in seed germination and seedling development studies are usually obtained with the use of several isothermal incubators. A thermogradient incubator measuring 15 by 36 by 54.5 cm and weighing less than 20 kg was built from 6.3–mm thick aluminum sheet. It was heated electrically at the top and cooled by circulating water at the bottom. It contained 12 equidistant (2.5 cm) sample compartments separated by fixed shelves. Each shelf supported a removable tray to accommodate a row of three standard petri dishes. The mean temperature gradient along the sample compartments (but excluding the cooling and heating compartments) was linear at all temperature differentials (T) tested. Settings for maximum heating at the top shelf and cooling at the bottom shelf gave approximately 54° and O°C, respectively, thus giving a AT of 54°C across the 12 sample compartments. With these settings, temperature cycling with time and temperature nonuniformity within a given shelf was higher for warmer (upper) shelves but negligible for cooler (lower) shelves. However, temperature cycling in the upper shelves was minimized by selecting smaller temperature differential(s). In addition to being more portable and less expensive than other reported devices, the incubator occupies less space and permits the use of standard petri dishes or paper towels in triplicates. Construction specifications for the thermogradient incubator are provided.

Key Words: Tobacco • Seedling • Temperature • Therma

² Senior researcher (reprint requests), Biol. & Agric. Eng. Dep, and assistant director of research, North Carolina Agric. Res. Service, North Carolina State Univ., Raleigh, NC 27695–7625, respectively.

Received for publication April 29, 1985.