DICE'CISM (front 1;k. Sr-, di-, double 4 oikos. house). Primarily this word applies to that condition in plants in which the male and female organs are borne by different indi viduals. In its original application, lawevcr, it referred to the fact that in some seed-plants the stamens and pistils are borne by separate Diweism in mosses and ferns, there fore, does not mean the same thing, as diu•cisin in seed plants. In the mosses and ferns it refers tr the fact that in certain species one gameto phyte (prothallinni in ferns) hears the anther idia and another the In seed-plants it refers to the fact that one sporophyte product's the stamens trnierosporophylls) nial another produces the earpels (megasporophylls). As flats applied, the name has no morphological significance; hunt in both eases it refers in it sense to a similar physiological condition. If the diteeism. as exhibited by mosses and ferns, be stri•tly traced into the seed-plants, it is dk eovered that they are all dbecions, for in 41 of them the male cells and eggs :ire produeed by different gametophytes. This is merely a result of het erospory, and lit-net' hoborm.porolis plants essentially diopions, if considered from the standpoint of the sox organs.
The significanee of the ditt•eism of seed-plants is not dear. although ninny see in it n condition which secures all of the advantages of cross pollination, On the other hand, it is in general a primitive condition, for many gyinine.perms and the most primitive angiosperms are dia. cions. Although prevailingly displayed by the more primitive groups of seed-plants, it is tes means wanting in the highest groups, so that it is not an essential indication of either a primi tive or a derived condition. There are eases in which it is evident that the diaTious 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 eases the diaTions condition has conic from what is called the bisporangiate condition—i.e. one in which the two sets of sporangia occur in the same flower. DiaTious flowers are necessarily mono sporangiate: but flowers may be monosporangiate and yet both kinds of flowers may occur upon the same individual. The monosporangiate and dice cions conditions are therefore not synonymous.