. Class-book of botany : being outlines of the structure, physiology and classification of plants : with a flora of the United States and Canada . Botany; Botany; Botany. THE LIGNEO0S SYaiBM. 139. 637, Eootlet of Madder, showing cells expanded into flbrilliE. 58S, Grlandular Iiair of Fraxi- nella, section. 589, Hair of Bryonia, of several cells. 590, Hair of several cells, surmounted by a gland, of Antirrhinum majus. 591, Sting of Urtica dioioa. 692, Jointed hair of the stamens of Tradescantia. , Stellate hair from the petiole of Nuphar advena (magnified 300 diameters, Henftey). 694, Branc
. Class-book of botany : being outlines of the structure, physiology and classification of plants : with a flora of the United States and Canada . Botany; Botany; Botany. THE LIGNEO0S SYaiBM. 139. 637, Eootlet of Madder, showing cells expanded into flbrilliE. 58S, Grlandular Iiair of Fraxi- nella, section. 589, Hair of Bryonia, of several cells. 590, Hair of several cells, surmounted by a gland, of Antirrhinum majus. 591, Sting of Urtica dioioa. 692, Jointed hair of the stamens of Tradescantia. , Stellate hair from the petiole of Nuphar advena (magnified 300 diameters, Henftey). 694, Branched hciir, one cell, of Arabis. OHAPTBK IV. THE LIGNEOUS SYSTEM 685. Includes the firm structures of roots, stems, and their append- ages, summarily called the wood. 686. Steuotokb. The growing rootlet of the germinating plant exhibits under a microscope a nearly uniform mass of cellular tissue. The cells composing it are soft and delicate, with thin, porous walls adapted to absorb moisture, which it has already begun to do. It grows by the accession of cell to cell through their divi- sion and enlargement at its point, or rather just behind the advance layer which constitutes its cap (pileorhiza § 725. 68Y. TnE EARLIEST TISSUE. The same structure also appears in the expanding cotyledons and the opening bud of the plumule. At this early stage, therefore, all plants alike in all their parts are composed of simple parenchyma. Subsequent changes in structure occur, giving to each tribe its several peculiarities. Still the growing points of the axis, both ascending and descending, advance by the format tion of the same tissue, and the vessels, if formed at all, follow a little later. 688. The changes. The rootlet soon becomes a root, assumes a corky layer in- stead of the tender, spongiform epidermis, and ceases to absorb; But new rootlets spring from the radicle, or branch from the axis, which in their turn absorb, harden, divide and subdivide; and so on indefinitely. 689. The is
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