On The Origin of Species by Charles Darwin Chapter 16 Page 13

DICOTYLEDONS, or DICOTYLEDONOUS PLANTS. — A class of plants characterised by having two seed-leaves, by the formation of new wood between the bark and the old wood (exogenous growth) and by the reticulation of the veins of the leaves.

The parts of the flowers are generally in multiples of five.

DIFFERENTATION. — The separation or discrimination of parts or organs which in simpler forms of life are more or less united.

DIMORPHIC. — Having two distinct forms. — DIMORPHISM is the condition of the appearance of the same species under two dissimilar forms.

DIOECIOUS. — Having the organs of the sexes upon distinct individuals.

DIORITE. — A peculiar form of Greenstone.