Pharmaceutical botany - Lighthouse Survival Blog
Pharmaceutical botany - Lighthouse Survival Blog
Pharmaceutical botany - Lighthouse Survival Blog
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26 PHARMACEUTICAL BOTANY<br />
or, (b) the outermost layer of cortex cells underneath the epidermis be-<br />
comes active after being passive for one year, and lays down walls, the<br />
inner layer becoming cork cambium, the outer becoming a layer of cork.<br />
The cork cuts off water and food supplies from epidermis outside and so<br />
epidermis separates and falls off as stringy layer. The cork cambium<br />
produces cork on its outer face and secondary cortex on its inner.<br />
Between the bundles certain cells of the primary medullary rays<br />
become very active and form interfascicular cambium which joins the<br />
cambium of the first-formed bundles (intrafascicular cambium) to form<br />
a complete cambium ring. By the rapid multiplication of these cam-<br />
bial cells new (secondary) xylem is cut off internally and new (secondary)<br />
phloem externally, pushing inward the first-formed, or protoxylem,<br />
and outward the first-formed, or protophloem, thus increasing the<br />
diameter of the stem. The primary medullary rays are deepened.<br />
Cambium may also give rise to secondary medullary rays.<br />
Sometimes, as in Grape Vines, Honeysuckles, and Asclepias, instead<br />
of cork cambium arising from outer cortex cells it may arise at any<br />
point in cortex. It is the origin of cork cambium at varying depths<br />
that causes extensive sheets of tissue to separate off. That is what<br />
gives the stringy appearance to the stems of climbers.<br />
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At close of first year in Perennial Dicotyl Stem we note<br />
1. Epidermis—development of dermatogen or periblem—in process of peeling<br />
off, later on entirely absent.<br />
2. Cork tissue or periderm.<br />
3. Cork cambium or phellogen.<br />
4. Sometimes zone of thin-waUed cells containing chloroplasts cut off by<br />
cork cambium on inner face known as phelloderm.<br />
5. Cortex—in perennial stem cells of cortex may undergo modification into<br />
mucilage cells, into tannin receptacles, crystal cells, spiral cells, etc.<br />
6. Fibrovascular bundles of open collateral type which are now arranged<br />
into a compact circle, and between which are found primary and often<br />
secondary medullary r^ys.<br />
From without inward the following tissues make up f. v. bundles.<br />
Protophloem j Hard Bast—long tenacious bast fibres.<br />
Secondary Phloem \ Soft Bast—phloem cells and sieve tubes.<br />
Cambium— active layer giving rise to secondary phloem on outer and secondary<br />
xylem on inner face, and adding to depth of med. rays.<br />
Secondary xylem—wood fibres, pitted vessels, tracheids.<br />
Protoxylem— spiral trachere.<br />
Pith.