. Comparative anatomy of the vegetative organs of the phanerogams and ferns. Plant anatomy; Phanerogams; Ferns. SECOXDA R y CHA XGES. 5. The phenomena described usually extend uniformly over the whole of the stem and its branches; examples, however, occur of differences in the formation of periderm in zones,at different heights. This is the case in Pinus sylvestris (p. 556), a tree which is distinguished by the thick bark on the lower stem, and the fine peeling bark on its apex and branches, from its allies, e. g. P. Laricio, in which the thick bark extends to the apex. According to Hartig thi
. Comparative anatomy of the vegetative organs of the phanerogams and ferns. Plant anatomy; Phanerogams; Ferns. SECOXDA R y CHA XGES. 5. The phenomena described usually extend uniformly over the whole of the stem and its branches; examples, however, occur of differences in the formation of periderm in zones,at different heights. This is the case in Pinus sylvestris (p. 556), a tree which is distinguished by the thick bark on the lower stem, and the fine peeling bark on its apex and branches, from its allies, e. g. P. Laricio, in which the thick bark extends to the apex. According to Hartig this is also the case in the Birch, in which the higher portions of the stem, and the branches, independently of their age, constantly remain covered by superficial periderm only. Sect. 179. Lcniiceh'^. In most woody plants which form periderm the uniform peridermal integuments hitherto described are interrupted at definite points, to be more exactly indicated below, by bodies which are as it were inserted in them and belong to them, to which De Candolle gave the name of Lefilkels, and Du Petit- Thouars the more descriptive one of cortical pores. Only in relatively few woody plants, provided with a regularly repeated annular formation of bark, have lenticels as yet been sought in vain: Vitis vinifera, Lonicera italica, L. periclymenum, Tecoma. FIG. 221.—Transverse section through the cortical surface of a shoot of Betula alba one year old (145). e. e epidermis, s stoma, rf glandular scale, ^—p superficial periderm, with a lenticel interpolated below the stoma. In the lenticel two firmer, denser tangential bands are visible; but the narrow intercellular spaces containing air are left undrawn m the whole of the lower part, on account of the low magnifying power. radicans, species of Clematis, Philadelphus and Deutzia, and Rubus odoratus, while, on the other hand, they appear in other plants, which are nearly related systematically to those mentioned, or agree with them in growth
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