this occurs in many fruit trees, poplars, elms and others.  For instance, the young shoots seen springing from the ground around an elm are not seedlings but root-shoots.  Frequently, as in many Dicotyledons, the primary root, the original root of the seedling, persists throughout the life of the plant, forming, as often in biennials, a thickened tap-root, as in carrot, or in perennials, a much-branched root system.  In many Dicotyledons and most Monocotyledons, the primary root soon perishes, and its place is taken by adventitious roots developed from the stem.

Flower.

The most characteristic feature of the Angiosperm is the flower, which shows remarkable variety in form and elaboration, and supplies the most trustworthy characters for the distinction of the series and families or natural orders, into which the group is divided.  The flower is a shoot (stem bearing leaves) which has a special form associated with the special function of ensuring the fertilization of the egg and the development of fruit containing seed.  Except where it is terminal it arises, like the leaf-shoot, in the axil of a leaf, which is then known as a bract.  Occasionally, as in violet, a flower arises singly in the axil of an ordinary foliage-leaf; it is then termed axillary.  Generally, however, the flower-bearing portion of the plant is sharply distinguished from the foliage leaf-bearing or vegetative portion, and forms a more or less elaborate branch-system in which the bracts are small and scale-like.  Such a branch-system is called an inflorescence.  The primary function of the flower is to bear the spores.  These, as in Gymnosperms, are of two kinds, microspores or pollen-grains, borne in the stamens (or microsporophylls) and megaspores, in which the egg-cell is developed, contained in the ovule, which is borne enclosed in the carpel (or megasporophyll).  The flower may consist only of spore-bearing leaves, as in willow, where each flower comprises only a few stamens or two carpels.  Usually, however, other leaves are present which are only indirectly concerned with the reproductive process, acting as protective organs for the sporophylls or forming an attractive envelope.  These form the perianth and are in one series, when the flower is termed monochlamydeous, or in two series (dichlamydeous).  In the second case the outer series (calyx of sepals) is generally green and leaf-like, its function being to protect the rest of the flower, especially in the bud; while the inner series (corolla of petals) is generally white or brightly coloured, and more delicate in structure, its function being to attract the particular insect or bird by agency of which pollination is effected.  The insect, &c., is attracted by the colour and scent of the flower, and frequently also by honey which is secreted in some part of the flower. (For further details on the form and arrangement of the flower and its parts, see FLOWER.)

Stamen and pollen.