Pharmaceutical botany - Lighthouse Survival Blog

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PHARMACEUTICAL BOTANY
and then smaller in calibre. These store starch and enable sap to pass
through.
3. Endodermis, or innermost layer of cells in the cortex with len-
ticularly thickened radial walls.
4. Pericambium, a zone of one, two, or three layers of rounded,
thin-walled, actively dividing cells, which may give rise to side rootlets.
5. Radial fibrovascular bundle, which in most monocotyledons
consists of eight, twelve, or fifteen alternating patches of phloem with
radiating xylem arms between. Phloem tissue consists of phloem cells
and sieve tubes. Xylem at tips of arms, made of spiral tracheae the
first xylem elements to mature. Internal to these are small pitted
vessels, later, striking pitted vessels and considerable wood fibre.
6. Pith.
Dicotyledons.— ^The typical dicotyl root is a tetrarch one, four
xylem alternating with four phloem patches. These roots have an
unlimited power of growth.
A. Of Primary Growth.
A trans-section of a dicotyl root in its young growth shows the fol-
lowing structure from periphery toward centre.
1. Epidermis with cutinized outer walls.
2. Hypodermis.
3. Cortex with usually small intercellular spaces.
4. Endodermis, or innermost layer of cells of the cortex with radially
thickened walls.
5. Pericambium of one to two layers of actively growing cells which
may produce side rootlets.
6. Radial fibrovascular bundle of four, rarely two or three or five
or six phloem patches alternating with as many xylem arms. Not
uncommon to find bast or phloem fibre along outer face of each phloem
patch. Xylem has spiral tracheae, internal to these a few pitted vessels.
Then, as root ages, more pitted vessels, also xylem cells and wood
fibres make their appearance
B. Of Secondary Growth. (Most ofiicial roots.)
At about six weeks one notes cells dividing by tangential walls in
the inner curve of phloem patches. This is intrafascicular cambium.
A single layer of flattened cells starts to cut off on its inner side a quan-
tity of secondary xylem and pushes out the patches of bast fibres, adds
a little secondary phloem on the outer side. Secondary xylem finally
fills up the patches between the arms. The patches of bast fibres get