Sex expression in spinach

Abstract does not appear. First page follows.

As would be expected in a dioecious, wind-pollinized plant, existing varieties of spinach are in general in a highly heterozygous condition. Commercial stocks are frequently of mixed varieties, of unsuitable types, or incorrectly named. These defects are the cause of much loss to growers and canners. Knowledge of the nature of the sexual conditions in spinach, as well as of the factors controlling sex expression, was considered essential to the work of plant breeding. There will be presented here, therefore, a description of the sexual conditions in spinach, together with results of certain experiments to test the relation of sex expression to ecological and physiological factors. The genetical aspects of sexuality in spinach will be dealt with in a later paper.

Position of Flower Clusters

After germination, spinach plants develop a rosette of eight or more leaves which arise from a much shortened stem (or “crown”) located just above the surface of the ground and surmounting the thick, fleshy tap root. When the plant reaches a certain size, with the coöperation of favorable environmental conditions, the stem begins to elongate rapidly. At the same time, lateral branches arise from the axils of the rosette leaves, and in some varieties, these laterals may in time exceed the central stem in size and height. Secondary lateral branches arise from the leaf axils of both central and lateral stems. On these secondary branches, as well as on the upper portion of the central and lateral stems, are borne the flower clusters. These clusters are borne axially both on the larger stems and on the smaller branches arising from the same axils. Flowering usually begins on the middle portion of the larger stems and proceeds toward the base and the tip.