Nature and development of plants . lar bundles. The monocotyledons, plants distinguished usually by theirparallel veined leaves and single seed leaf, like the palms, lilies,ses, etc., are characterized by stems that do not increasematerially in diameter. Growth is largely confined to the topof the stem and consequently it can only elongate, forming avery regular, columnar trunk. The reason of this is apparentwhen cross sections of such stems are examined I Fig. 45. D).The vascular bundles are more or less scattered throughout thestem and it is especially noteworthy that there is no cambium sep
Nature and development of plants . lar bundles. The monocotyledons, plants distinguished usually by theirparallel veined leaves and single seed leaf, like the palms, lilies,ses, etc., are characterized by stems that do not increasematerially in diameter. Growth is largely confined to the topof the stem and consequently it can only elongate, forming avery regular, columnar trunk. The reason of this is apparentwhen cross sections of such stems are examined I Fig. 45. D).The vascular bundles are more or less scattered throughout thestem and it is especially noteworthy that there is no cambium separating the xylem and phloem. It will he seen by examining Fig. x. that the tissues of the bundles are of a similar characterand have the same arrangement as in the dicotyledons ( Fig. 41) save for the absence of the cambium which prevents the addition of new cells to the xylem and phloem. Consequently there canbe no considerable increase in the diameter of the stem and nonecessity therefore for the protective layer of cork e c x * Fig, 61. Longitudinal Bection of the tip of a growing stem: .. epidermisding over surface of the entire tip; a, formative region; b, upperportion of the rone of elongation; c, cortex; x, cells of the central 1that by further growth form the vascular bundles; /, first appearaithe le 41. Apical Growth of the Stem.— All stems are characterizedby a more or less extended apical growth. The changes pro-duced in stems by the growth of the cambium onlj result inincreasing their diameters bul the elongation of all stems is NATURE OF PLANTS 83 effected by the formation of new cells at the apex of the 61 shows the general features to be noticed in the tip ofa stem as seen in longitudinal section. New cells are beingformed at the apex by division just as in the case of the this formative region is the zone of elongation in whichthe cells gradually change in character so that the cortical and
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