In the last week of May I have found the bigtoothed aspen catkins open, the two valves of the capsule rolled back, and, clinging to the withered catkin, the bunches of hairs containing the minute seeds almost invisible to the naked eye. Unlike the poplars the fruiting catkins of the birches are stiff and usually sit erect upon the stem, resembling little cones. They consist of alternating layers around the central axis of quaint, three-lobed scales and dainty, two-winged, little brown seeds more easily studied with the magnifier. Each kind of birch seed has a pair of styles attached to the end of the seed between the shoulders of its gauzy wings; those of the sweet birch are most prominent and easily seen. When the fruits are ripe and the catkins fall apart these light, insect-like seeds are wafted far and near.

No two kinds of birch seeds are winged just alike; each three-lobed protecting scale has its own characteristic shape, the gray birch resembling the outline of a bird on the wing. The yellow birch catkins are the thickest, those of the gray birch are more nearly cylindrical and stay on the trees longest, the river birches have the largest seeds inside and are the only ones with downy, margined wings. Just why Nature tucks the winged birch fruits under the protecting scales of a charming little cone and lets the delicate, winged fruits of the elm hang in clusters exposed to the elements we do not know. The white elm and the English are the most prolific. In one cluster taken from an American elm I have counted two dozen fruits that have developed from the flowers coming from one bud.

The whole fruit, about three-eighths of an inch long, attached to a short, slender stem, is flat, and consists of a thin wing, nearly elliptical in outline, with a circular notch in the outer end, and a central sac-like portion containing a tiny seed which can be seen when the fruit is held to the light. The margin of the wing is thickly fringed with fine, white hairs. The English elm fruits are two-thirds again as large, almost circular, with a much larger proportion of thin, gauzy wing and a less evident slit-like notch; the small hollow central part contains a smaller seed. No hairs can be seen even with a magnifier.

The slippery elm fruits come between these two in size. They have no noticeable notch in the gauzy wing, and have hairs only in the hollow part that holds the seed. Those of the rock elm are thicker in texture and are entirely covered with soft white hairs. The spatula or paddle-shaped winged fruit of the ash, with the seed at one end of the paddle, is distinctive. The white ash paddles grow on diverging stalks, dividing by threes, making the group sometimes from five to seven inches long. They are abundant and very noticeable even when green like the leaves.