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Conifers

These are trees or bushes that bear cones. Common conifers include the cypresses, cedars, Douglas fir, junipers, larches, spruces and Scot's pine. Botanists know of some 600 species of conifers which make up an important part of the vegetation of the cooler parts of the world. Although they do not compare in numbers with the much longer 250,000 strong list of flowering plant species, conifers do include two unique record-holders: the largest and the oldest living things. Some redwoods of the western United States tower more than 300 feet into the sky. Also in the United States, bristle-cone pines up to 5,000 years old still live and flourish.

Some conifers have a single, un-branched trunk. The leaves of conifers vary considerably in arrangement and in appearance. A fir tree has needle-like green leaves which densely clothe the branches. Pine trees have two kinds of leaves, needle-like, green foliage leaves and small, brown scale leaves. The green needles grow singly, in pairs, or in groups of up to five, depending on the species. Some conifers have scale-like green leaves which overlap each other and lie close to the stems.

Most conifers are evergreens and their leaves are well adapted to the cold conditions in which the majority of these trees live. Cold winter winds tend to draw water from the plants, but when the soil is frozen the plants cannot replace lost water so easily. Plants of cold regions therefore need fairly compact leaves, with a relatively small surface area through which they can lose water. This is just what the needle-shaped conifer leaves provide. In addition, the leaves have a thick, waxy coating (cuticle) and their pores, or stomata, are sunk below the surface. These two features discourage water loss even further. Some conifers go one stage further still and drop all their leaves in the autumn. The larches are examples of these deciduous conifers. The evergreen conifers do drop their leaves of course, but not all at once.

The stem, or trunk, of a conifer is much the same as that of flowering plants, except that conifers conduct water through dead cells called tracheids. Neighboring tracheids are not joined together to form long tubes as xylem vessels are in flowering plant stems. There are holes (pits) in the tracheid walls and water flows through these pits.

Conifers reproduce by means of sex cells produced in specialized structures called cones. In the Scots pine (Pinus sylvestris), a very common example, male and female cones develop on the same tree. Male cones are yellow clusters of scales arranged spirally around a central stem. Each scale bears two pollen sacs on its underside. In early summer, clouds of pollen are blown by the wind to the young female cones, which look like pinkish buds at the tips of young shoots. Female cones consist of spirally arranged scales. The upper part of the scales bears the ovules. Although pollen reaches the female cone safely enough, fertilization does not take place in the Scots pine until the following year, and the seeds do not ripen until a year after that. The seeds are scattered by the wind as they fall from the open cone.