. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. PARENCHVMA. 117 The forms of thin-walled parenchymatous cells are in the main nearly iso-dia- raetric; but there often occur also elongated-prismatic, spindle-shaped cells, and the like, examples of which, e. g. in the case of the vascular bundles, will be described later; to this category belong also those chlorophyll-containing cells arranged in many leaves perpendicular to the surface, forming the pallisade parenchyma, to be described in Chapter IX. As above intimated, very great variety of s
. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. PARENCHVMA. 117 The forms of thin-walled parenchymatous cells are in the main nearly iso-dia- raetric; but there often occur also elongated-prismatic, spindle-shaped cells, and the like, examples of which, e. g. in the case of the vascular bundles, will be described later; to this category belong also those chlorophyll-containing cells arranged in many leaves perpendicular to the surface, forming the pallisade parenchyma, to be described in Chapter IX. As above intimated, very great variety of shape is found among the iso-diametric forms. It is only in definite single cases, e. g. in hypodermal sap-parenchyma, that the cells are of such form that all of them are bounded by flat surfaces and sharp edges, and therefore are in uninterrupted connection with one another. As a rule the surface of the parenchymatous cells is more or less rounded, or bears irregular protuberances, or the protuberances themselves are drawn out into long arms: in this case they are mutually connected only by definite parts of their surface, which vary in size accord- ing to the special form. Between them intercellular spaces are left free. Masses of parenchyma in which the latter (which are then usually filled with air) are developed to a great extent are distinguished as lacunar parenchyma, or, comparing it with a bath-sponge, spongy-parenchyma. Compare Chapters VII and IX. The walls of the cells of this category are as a rule cellulose membranes, with ordinary simple pitting. The latter, following the general rule, usually occurs only on the parts of the surface in contact with that of other cells: in cases then where the cells show a decided partial rounding off, and only touch one another with narrowly limited parts of their surface, or only with the ends of protuberances, the pits lie on these spots, and not on the rest of the wall. As regards the surfaces of contact, the same may also occ
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