Short notes on Secretory tissue and Kinds of vascular bundles,
SECRETARY TISSUES
(i) Latiferous tissue: This
consists of thin walled greatly elongated much branched ducts containing a
milky juice the latex. Latiferous ducts are of two kinds latex vessels and
latex cells. They contain numerous nuclei which lie embedded in thin lining
layer of protoplasm. They occur irregularly distributed in the mass of
parenchymatous cells. They mat act as food storage organs or as reservoirs of
waste products. They also act as translatory tissues.
Latex Vessels: They are rows of
more or less parallel ducts connected with one another by the fusion of
branches forming a network. Latex vessels are found in poppy family. E.g. opium
poppy, garden poppy and prickly poppy and also in some species of sunflower
family e.g. sonchus.
Latex Cells: They are really
single or independent units. They branch through parenchymatous tissue of the
plant.
KINDS OF VASCULAR BUNDLES
On the basis of arrangement of
xylem and phloem vascular bundles are of following kinds.
(i) Radial: When xylem and phloem
form separate bundles and these lie on different radii alternating with each
other as in roots.
(ii) Conjoint: When xylem and
phloem combine into one bundle. Conjoint are three types.
(a) Collateral: When xylem and
phloem lay together the same radius, xylem being internal and phloem external.
When in a collateral bundle the cambium is present as in Dicot stems. The
bundle is said to be open and when the cambium is absent it is said to be
closed as in Monocot stems.
(b) Bicollateral: when in a
collateral bundle both phloem and cambium occur twice, once on the outer side
of xylem and then again on its inner side. The sequence is outer phloem, outer
cambium, xylem, inner cambium and inner phloem. Bicollateral bundle is example
of the gourd family. It is always open.
(c) Concentric: When the xylem
lies in the centre and is surrounded by phloem as in ferms of phloem lies in
the centre and is surrounded by xylem e.g. monocot as in sweet flag.
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