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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