. The essentials of botany. Botany. THE TISSUES OF PLANTS. 23 Tracheary tissue is found only in ferns and their rela- tives and the flowering plants. The principal varieties of vessels found in tracheary tissues are the following: 49. (1) Spiral Vessels, which are usually long, with fusi- form extremities; their walls are thickened in a spiral man- ner with one or more simple or branched bands or fibres (Fig. 15, v", v'", v""). This form may be regarded as the typical form of the vessels of tracheary tissue. Ringed and reticulated vessels are opposite modifications of tl~-
. The essentials of botany. Botany. THE TISSUES OF PLANTS. 23 Tracheary tissue is found only in ferns and their rela- tives and the flowering plants. The principal varieties of vessels found in tracheary tissues are the following: 49. (1) Spiral Vessels, which are usually long, with fusi- form extremities; their walls are thickened in a spiral man- ner with one or more simple or branched bands or fibres (Fig. 15, v", v'", v""). This form may be regarded as the typical form of the vessels of tracheary tissue. Ringed and reticulated vessels are opposite modifications of tl~- spiral form; the first are due to an under-development of. Fig. 15.—Lonsitudmal section of a portion of the stem of Garden Balsam (Im- patiens). v, a ringed vessel; «', a vessel with rings and short spirals; «", a ves- sel with two spirals; «'" and «"", vessels with branching spirals; v"'", a vessel with iiTegular thickenings, forming the reticulated vessel. the thickening in the young vessels, resulting in the pro- duction here and there of isolated rings (Fig. 15, «); reticu- lated vessels are due, on the contrary, to an over-develop- ment, which gives rise to a complex branching and anas- tomosing of the spirals (Fig. 15, v'""). 50. (2) Scalariform Vessels.—These are prismatic ves- sels whose walls are thickened in such a way as to form transverse ridges. They are wide in transverse diameter, and their extremities are fusiform or truncate (Fig. 16). 51. (3) Pitted Vessels.—The walls of thefie vessels are thi6ken6d in such a way as to give rise to pits aa4 Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bessey, Charles E. (Charles Edwin), 1845-1915. New York, Holt
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