(a) Apetalæ—These include families of plants that are the simplest in structure of all the dicotyledons. In all of them there are no petals and in some both petals and sepals are lacking, leaving only essential organs. Taking first those families that have neither petals nor sepals we find that most of them bear their flowers in catkins, a flower cluster familiar enough in the pussy willow. Some of these families are the following:
Juglandaceæ—Trees with compound leaves, flowers in catkins and fruits inclosed in a thick husk. Examples: walnut and hickory. Six genera and over 30 species.
Salicaceæ—Shrubs or trees with simple leaves, flowers in catkins and capsular many-seeded fruits, but no nuts. Containing only willows and poplars. Two genera and over 200 species. ([Figure 93].)
Myricaceæ—Shrubs or trees with simple usually fragrant leaves, flowers in catkins and fruits one-seeded. The bayberries. Two genera and about 35 species. ([Figure 94].)
These and some other families of close relationship are the least developed, in their flower structure, of any of the dicotyledons. All of them bear only the essential organs of reproduction in their very simple flowers. In the walnuts and hickories the different sexes are in different flowers on the same plant, in the willows they are even on different plants, and in Myricaceæ they are often found both ways. All of these flowers are wind-pollinated, so that they bear no honey, usually have no odor, and of course their need for showy petals for attracting insects is nil, although some pollen-eating insects visit them.