Text-book of structural and physiological botany . allyair. In the Asclepiadeaeand Apocynacese they con-tain a peculiar greenish saprelated to the latex of otherplants. The bast-paren-chyma agrees almost en-tirely in its developmentand structure with thexylem. The vessels of thebast are sieve-tubes or lati-ciferous vessels. The presence or ab-sence, and the arrangement,of the separate elements inthe cortex, are so charac-teristic of most stems thatthey can be determinedfrom these characters. Ageneral idea may be ob- FiG. 476. — Part of a transverse section foinpri \\\t q f-rnnc:\7Prcz:^ c^r-th
Text-book of structural and physiological botany . allyair. In the Asclepiadeaeand Apocynacese they con-tain a peculiar greenish saprelated to the latex of otherplants. The bast-paren-chyma agrees almost en-tirely in its developmentand structure with thexylem. The vessels of thebast are sieve-tubes or lati-ciferous vessels. The presence or ab-sence, and the arrangement,of the separate elements inthe cortex, are so charac-teristic of most stems thatthey can be determinedfrom these characters. Ageneral idea may be ob- FiG. 476. — Part of a transverse section foinpri \\\t q f-rnnc:\7Prcz:^ c^r-through the bast of the wild lettuce, Lac- ^^^^^Q Dy a traUSVCrSC SeC-tuca scariola ; b/ bast fibres; b^ bast tioU thrOUffh a baSt-buudlcparenchyma ; m outer, m inner laticifer- y ous vessels ; R/ cortical parenchyma ; h^ of the wild IcttUCC ( (x 400). \ o 476). In woody Dicotyledons the pith .and the parts of thecortex which do not belong to the vascular bundles are veryinconsiderable in comparison with these latter. The pith of. special Morphology and Classification, 369 the stem only increases for a short time, and then only bythe increase in size of the separate cells, and occupies there-fore but a small space in comparison with the wood and thefundamental tissue of the medullary rays. It consists of aparenchymatous tissue, in which other elements, as latici-ferous vessels, are sometimes, though rarely, enclosed. Deviations are not unfrequent from the normal structure and courseof the vascular bundles here described. In many water-plants, such asHippuris^ Myriophyllum, Ceratophyllum^ and Trapa, a sheath is formedwhich limits the increase in diameter of these plants. (Fig. 94, p. 66.) The roots of Dicotyledons always possess, when young,a thin-walled epidermis, which soon becomes replaced, likethat of the stem, by cork-tissue. The cortex of the rootis also very similar to that of the stem, consisting of thesame elements; and its cells contain the same substanc
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