. Class-book of botany: being outlines of the structure, physiology and classification of plants; with a flora of the United States and Canada. Botany; Plants; Plants. 136 THE TISSUES. £S0 contiguous walls. This tissue varies according to trie character of the constituent cells, which are (a) spiral, or (b) annular, or (c) sclariform, or (d) reticulated. 669. Such cells, with their tapering ends, form vessels with obliquo joints. When porous cells (653) with their truncated ends unite they form right-jointed vessels re- sembling strings of beads, called doited or vascular ducts. These are usua
. Class-book of botany: being outlines of the structure, physiology and classification of plants; with a flora of the United States and Canada. Botany; Plants; Plants. 136 THE TISSUES. £S0 contiguous walls. This tissue varies according to trie character of the constituent cells, which are (a) spiral, or (b) annular, or (c) sclariform, or (d) reticulated. 669. Such cells, with their tapering ends, form vessels with obliquo joints. When porous cells (653) with their truncated ends unite they form right-jointed vessels re- sembling strings of beads, called doited or vascular ducts. These are usually quite large, and characteristic of the woody layers of all exogenous plants. (470.) 670. The different varieties of trachenchtma are assigned to different re- gions and offices, (a) to the earliest formed part of the wood, the petioles and veins of leaves, petals of flowers, etc.; (b) to similar parts, but later formed, most abundant in ferns and Eqmsetaee;e; (c) in the woody bundles of the Endogens and in the succu- lent parts of plants in general; (d) most abundant in ferns, club-mosses. 671. Cienchvma is a system of milk-vessels—vessels secreting the latex or peculiar juice of the plant, white, yellow, red, turbid, containing opium, gamboge, caoutchouc, resin, etc. It occurs in the petioles and veins ; in the parenchyma of roots, in the liber es- pecially ; sometimes simple, generally branched and netted in a complicated manner, as well seen in the poppy, ce- landine, blood-root, gum-elastic tree, etc. « These vessels are probably mere open spaces between the cells at first, subsequently acquiring a lining membrane which never exhibits pores or spiral markings. But there are also true 673. Intercellular passages filled with air and admitting its free circulation in all directions through the parenchyma. These are neces- sarily very irregular, and they communicate with the external air through the stomata. (§ 678.) 674. Import of the cell. Thus the cell appears to be
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