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ne ANOMALOUS PRIMARY "STRUCTURES', , Internal organization of various tissues usually exhibit a set pattern in most phetearanns, and dicotyledonous stems. These are called normal structures. However, a = Wa slighy Be, a greater ‘amount of deviation from the normal set pattern of the arrangement tau © AeViationg, in the primary structures of stems are regarded as anomalous primary struc’ i, , The anomalous primary structures are found both in monocotyledonous asl dicotyledonous stens, and, therefore, they are separately discussed below under the two main headings :—, , > [A] ANOMALOUS! PRIMARY STRUCTURES IN|) MONOCOTYLEDONOUS STEMS, , Normal primary structure of monocot stems is characterized by the presence of scattered vascular, bundles in the parenchymatous ground tissue where the cortex, endodermis, pericycle, medullary rays ang, pith are not differentiated. The vascular bundles are conjoint, collateral, closed and endarch. Each vascular, bundle is surrounded by sclerenchymatous bundle sheath. Such normal primary structures are found in, most of the monocotyledonous stems. However, some members show deviations from these normal, structures which are categorized as follows —, , (a) ARRANGEMENT OF VASCULAR BUNDLES IN TWO OR MORE DEFINITE RINGS:, , In some monocotyledons, the vascular bundles are arranged in distinct rings. Examples, Jamur, communis, Triticum (wheat), Hordeum (barley), Oryza (rice), Secale (rye), Avena (oat), etc. In Tamus, communis the vascular bundles are arranged in two rings. The ouler ring consists of smaller bundles, originating in the pericycle and the inner ring consists of larger bundles (Fig. 5.16)., , (6) PRESENCE OF DISTINCT CORTEX, ENDODERMIS, PERICYCLE AND PITH:, , In some monocotyledons the stems are differentiated into distinct cortex, endodermis, pericycle and, pith. Examples, Tamus communis (Fam. Dioscoreaceae), Asparagus (Fam. Liliaceae), ete., , , , , , , , OF INNER RING, , , , , Selle dels LT UUFIGURE SS ae areas, Tamus communis. Diagrammatic ¢.4. of stem showing arrangement of vascular }y, , IPT arse “Ath, , Muah, , undies in two rings., > [B}) ANOMALOUS ‘PRIMARY STRUCTURES IN’ DICOTYLEDONOUS' sTpyys, , Normal primary structure of dicot stems is characterized by — (#) the differentiation of distinct, epidermis, cortex, endodermis, pericycle and pith ; (if) The vascular bundles are conjoiny, ailtuaeh ek, , I

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cn no! ., os son ses Ho avever, some members sh rmal primary Structures are found in most of the, (1) Presence of scattered vascular bundles,, (2) Presence of vascular bundles in the Cortex (cortical bundl, (3) Presence of vascular bundles in the pith (Medullary vealen, (4) Presence of intraxylary or internal phloem, ., (5) a _ — — and phloem bundles,, 6) Absence of vessles in the i, par OF <The nee, , In some dicotyledons, the vascular bundles i, 5 . ‘ are scattered in the parenchymatous pround, Example, Peperomia langsdorfii (Fam, Piperaceac), Podophyllum (Fam. Poiddphyllscenc), Thatlicias, , and Anemone (Fam. Ranuncul, Sviepbaraceae) aceac), Papaver orientale (Fam. Papaveraceac), Nymphaea (Fam., , , , , , , , ; FIGURE)5:17,, Diagrammatic t.s. of stems showing scattered vascular bundles in, Peperomia langsdorfii (A) und Anemone (B),, , , , , , , , , , (2) PRESENCE OF VASCULAR BUNDLES IN THE CORTEX (CORTICAL BUNDLES) ;, , In some dicotyledonous stems, the vascular bundles are present in the cortex. These bundles are, called cortical eins, The cortical bundles are present in addition to normal ring of vascular bundles., Morphologically, they are the leaf trace bundles which traverse through the cortex before entering into the, leaf petioles. Presence of cortical bundles have been reported in more than thirty families of angiosperms., Somsof the ini t examples are — Nyctanthes arbortristis (Fam. Oleaceac), Casuarina (Family, C Es e onium vulgare (Fam. Plumbaginaceae),, , In Nyctanthes, the stem has squarish outline with four prominent angles. Single cortical bundle is, located sf ea angle of squarish stem. The cortical bundles of Nyetanthes are inversely oriented, i.e,, phloem lies towards inner side and xylem towards the epidermis (Fig. 5.18), In Casuarina, the number of, cortical bundles ‘corresponds to the number of ridges, Each cortical bundle is normally oriented, /.e.,, phloem lies towards outer side and xylem towards inner side (Fig, 5.19). In Limonitum valgare, the, cortical bundles are numerous and scattered irregularly,