Abies balsamea

Abies balsamea or balsam fir is a North American fir, native to most of eastern and central Canada (Newfoundland west to central Alberta) and the northeastern United States (Minnesota east to Maine, and south in the Appalachian Mountains to West Virginia). It is celebrated for its rich green needles, natural conical shape, and needle retention after being cut, and it is notably the most fragrant of all Christmas tree varieties. Balsam fir is a small to medium-size evergreen tree typically 14–20 metres (46–66 ft) tall, occasionally reaching a height of 27 metres (89 ft). The narrow conic crown consists of dense, dark-green leaves. The bark on young trees is smooth, grey, and with resin blisters (which tend to spray when ruptured), becoming rough and fissured or scaly on old trees. The leaves are flat and needle-like, 15 to 30 mm (5⁄8 to 1 1⁄8 in) long, dark green above often with a small patch of stomata near the tip, and two white stomatal bands below, and a slightly notched tip. They are arranged spirally on the shoot, but with the leaf bases twisted so that the leaves appear to be in two more-or-less horizontal rows on either side of the shoot. The needles become shorter and thicker the higher they are on the tree. The seed cones are erect, 40 to 80 mm (1 1⁄2 to 3 1⁄4 in) long, dark purple, ripening brown and disintegrating to release the winged seeds in September. The male reproductive organs generally develop more rapidly and appear sooner than the female organs. The male organs contain microsporangia which divide to form sporogenous tissue, composed of cells which become archesporial cells. These develop into microspores, or pollen-mother cells, once they are rounded and filled with starch grains. When the microspores undergo meiosis in the spring, four haploid microspores are produced which eventually become pollen grains. Once the male strobilus has matured the microsporangia are exposed at which point the pollen is released. The female megasporangiate is larger than the male. It contains bracts and megasporophylls, each of which contains two ovules, arranged in a spiral. These then develop a nucellus in which a mother cell is formed. Meiosis occurs and a megaspore is produced as the first cell of the megagametophyte. As cell division takes place the nucleus of the megaspore thickens, and cell differentiation occurs to produce prothallial tissue containing an ovum. The remaining undifferentiated cells then form the endosperm. When the male structure releases its pollen grains, some fall onto the female strobilus and reach the ovule. At this point the pollen tube begins to generate, and eventually the sperm and egg meet at which point fertilization occurs.