The New International Encyclopædia/Diœcism

​DIŒ′CISM (from Gk. δι-, di-, double + οἶκος, oikos, house). Primarily this word applies to that condition in plants in which the male and female organs are borne by different individuals. In its original application, however, it referred to the fact that in some seed-plants the stamens and pistils are borne by separate individuals. Diœcism in mosses and ferns, therefore, does not mean the same thing as diœcism in seed-plants. In the mosses and ferns it refers to the fact that in certain species one gametophyte (prothallium in ferns) bears the antheridia and another the archegonia. In seed-plants it refers to the fact that one sporophyte produces the stamens (microsporophylls) and another produces the carpels (megasporophylls). As thus applied, the name has no morphological significance; but in both cases it refers in a sense to a similar physiological condition. If the diœcism, as exhibited by mosses and ferns, be strictly traced into the seed-plants, it is discovered that they are all diœcious, for in all of them the male cells and eggs are produced by different gametophytes. This is merely a result of heterospory, and hence heterosporous plants are essentially diœcious, if considered from the standpoint of the sex organs.

The significance of the diœcism of seed-plants is not clear, although many see in it a condition which secures all of the advantages of cross-​pollination. On the other hand, it is in general a primitive condition, for many gymnosperms and the most primitive angiosperms are diœcious. Although prevailingly displayed by the more primitive groups of seed-plants, it is by no means wanting in the highest groups, so that it is not an essential indication of either a primitive or a derived condition. There are cases in which it is evident that the diœcious habit is a derived one, since in the stamen-bearing flowers rudiments of the carpels may be found, and in the carpel-bearing flowers rudiments of stamens often occur. It is evident that in such cases the diœcious condition has come from what is called the bisporangiate condition—i.e. one in which the two sets of sporangia occur in the same flower. Diœcious flowers are necessarily monosporangiate; but flowers may be monosporangiate and yet both kinds of flowers may occur upon the same individual. The monosporangiate and diœcious conditions are therefore not synonymous.