Dicho'tomous

Dicho'tomous (Gr., 'divided into two equal parts'), a term formerly vaguely used in botanical description to designate any appearance of branching by forking. Thus the stems of some phanerogams—e.g. mistletoe, doum palm, and many inflorescences—e.g. Caryophyllæ, Begonias—appear forked, while an ordinary fern-frond has no such appearance. The progress of morphological research has, however, shown that true dichotomy—i.e. complete division of the growing point into two lateral apices, is really as characteristic of the development of the fern-frond as of such obviously dichotomous vegetation as that of Selaginella; while conversely the appearance of forking in phanerogams comes about simply by the suppression of the growing point, and the development of two new axes from opposite lateral buds. Outside the cryptogams, indeed, no case of true dichotomy has been described, with the doubtful exception of the roots of cycads. See CRYPTOGAMIA, FERNS, INFLORESCENCE, CYCADS, &c.