The Burpee Seed Company publishes "Seed Starter," by Maureen Heffernan (MacMillian, 1997, $19.95). The instructions for all aspects of starting seeds indoors and out are clear and well-illustrated. Although the seed varieties listed are those sold by Burpee, the instructions are applicable to other varieties as well.
For those fascinated by botany but daunted by technical accounts, "Botany for Gardeners," by Brian Capon (Timber Press, 1990, $17.95) is written in layman's terms. Capon explains plant structure, growth, reproduction, and how these should influence your gardening.