Stream Corner

Wind-pollinated plants produce vast amounts of pollen because most of it falls by the way and does not reach the flower and pistil. When the pine or spruce are in bloom huge clouds of pollen are carried by the wind and a layer of yellow dust covers the surface of nearby puddles and ponds. The pollen grains of most wind-pollinated trees have air sacs which make it possible for them to be carried as much as ten to twenty kilometres.

In the case of trees without air sacs (larch,Douglas fir, walnut) the pollen grains can be carried only several tens of metres and the trees produce a large number of barren seeds. Trees pollinated by insects produce a far smaller quantity of pollen, as more of the grains manage to reach their intended destination on the body of the insect.

In addition to these there are various compound flower itrrangements comprising several of the various simple types of inflorescence. The flowers of most trees are much less conspicuous and less brightly coloured than those of shrubs and herbaceous plants.

Each pollen grain germinates on the stigma, tiding down a tube into the ovary. This tube carries the intents of the pollen grain (nucleus) to an ovule, with which it fuses. After the male and female cells have fused, it seed begins to develop and the ovary eventually becomes the fruit.

Wind-pollinated trees such as the poplar, aspen, alder and hornbeam blossom early in spring, before the crown is in leaf, when the pollen can be distributed much more easily.

Individual trees start to produce seeds on attaining a certain age, usually one that is fairly advanced. Trees growing in forests usually start some ten to fifteen years later than those growing solitarily. The seed-bearing age of alders, birches and larches growing solitarily is about ten years, that ofsome maples, the Douglas fir and spruces twenty to thirty, and that of the silver fir and beech thirty to fifty years.