The Manual of the Botany of the Northern United States / Including the District East of the Mississippi and North of North Carolina and Tennessee

by Asa Gray

Class I. DICOTYLEDONOUS or EXOGENOUS PLANTS.

Stems formed of bark, wood, and pith; the wood forming a layer between the other two, increasing, when the stem continues from year to year, by the annual addition of a new layer to the outside, next the bark. Leaves netted-veined. Embryo with a pair of opposite cotyledons, or rarely several in a whorl. Flowers having their parts usually in fives or fours.