REPRODUCTIVE SYSTEM, PLANT

any of the systems, sexual or asexual, by which plants reproduce. In plants, as in animals, the end result of reproduction is the continuation of a given species, and the ability to reproduce is, therefore, rather conservative, or given to only moderate change, during evolution. Changes have occurred, however, and the pattern is demonstrable through a survey of plant groups. Reproduction in plants is basically either asexual or sexual. Asexual reproduction in plants involves a variety of widely disparate methods for creating new plants identical in every respect to the parent. Sexual reproduction, on the other hand, depends on a complex series of basic cellular events, involving chromosomes and their genes, that take place within an elaborate sexual apparatus evolved precisely for the creation of new plants in some respects different from the two parents that played a role in their production. (For an account of the common details of asexual and sexual reproduction and the evolutionary significance of the two methods see reproduction.) In order to describe the modification of reproductive systems, plant groups must be identified. One convenient classification of organisms sets plants apart from lower forms such as bacteria, algae, fungi, and protozoans. Under such an arrangement, the plants, as separated, comprise two great divisions (or phyla)the Bryophyta (mosses and liverworts) and the Tracheophyta (vascular plants). The vascular plants include four subdivisions: the three entirely seedless groups are the Psilopsida, Lycopsida, and Sphenopsida; the fourth group, the Pteropsida, consists of the ferns (seedless) and the seed plants (gymnosperms and angiosperms). A comparative treatment of the two patterns of reproductive systems will introduce the terms required for an understanding of the survey of those systems as they appear in selected plant groups. Additional reading Investigations of plant reproductive systems are included in David W. Bierhorst, Morphology of Vascular Plants (1971), at an advanced level, with many photographs and an extensive bibliography; Mary F. Willson, Plant Reproductive Ecology (1983); Harold C. Bold and John W. La Claire II, The Plant Kingdom, 5th ed. (1987), an account of the structure and reproduction of representative plant types; Harold C. Bold, Constantine J. Alexopoulos, and Theodore Delevoryas, Morphology of Plants and Fungi, 5th ed. (1987), a profusely illustrated textbook designed for the advanced undergraduate and beginning graduate student; and Jon Lovett Doust and Lesley Lovett Doust (eds.), Plant Reproductive Ecology: Patterns and Strategies (1988). Harold C. Bold The Editors of the Encyclopdia Britannica