Paper Birch Tree

Those are the catkins, or tree flowers! see below

Paper Birch is monoecious, producing both male (staminate) and female (pistillate) flowers on the same tree; both types of flowers are organized into catkins. Premature forms of the catkins first develop during the fall, overwinter in a dormant state, and become mature during the spring as the leaves develop. Mature male catkins are 2-4" long, cylindrical in shape, and yellowish; they are usually arranged in groups of 3 and droop from the twigs near their tips. Each male catkin has numerous tiny flowers less than 1/8" across; the male flowers are arranged in clusters of 3 behind tiny bracts. Individual male flowers consist of a tiny 4-lobed calyx and 2 stamens (there are no petals). Mature female catkins are 1-2" long, narrowly cylindrical in shape, and greenish; they are ascending, rather than drooping, and develop individually near the tips of twigs. On each female catkin, the female flowers are organized into clusters of 2-3 behind tiny bracts. Individual bracts have 3 upper lobes that are divergent and they are usually ciliate or pubescent. Individual female flowers consist of a naked ovary with a pair of styles; they are less than 1/8" across. The flowers are cross-pollinated by the wind during the spring. Afterwards, the male catkins wither away, while the female catkins droop downward and become cone-like in appearance from the hardening of the bracts. The female flowers are replaced by small nutlets with lateral wings that are membranous and slightly wider than the nutlet. These winged nutlets are usually dispersed by the wind during the autumn; they can also be blown across the snow or transported by water.

Paper Birch
Betula papyrifera
Birch family (Betulaceae)
http://www.illinoiswildflowers.info/tree...