Anamalous secondary growth

Plants shows secondary anomalous behaviour in secondary growth region.

1. TOPIC:- ANOMALOUS SECONDARY GROWTH Under the supervision of:- Presented BY:- Dr. NIMISHA AMIST FACULTY OF BOTANY UNIVERSITY OF ALLAHABAD SALMAN KHAN M.Sc-2 nd SEM DEPARTMENT OF BOTANY UNIVERSITY OF ALLAHABAD

2. Anomalous Secondary Growth Anomalous secondary growth is the result of deviation in the cambial activity from the normal type found in most of the dicot. Haberlandt classified anomalous secondary growth into- adaptive and non-adaptive anomaly. Adaptive anomaly includes lianas which are woody climbers of tropics. Non adaptive anomaly includes anomaly of Rumex, Boerhaavia, Bougainviella, Mirabilis, Chenopodium etc .

3. Types of Anomalous Secondary Growth 1-Abnormal behaviour of normal cambium:- (A) The cambium forms vascular tissues only in the region of vascular bundle. (B) The cambium forms usually large proportion vascular tissues only in the region of vascular bundle. (C) The cambium forms irregular patches of parenchyma in xylem 2-Abnormal behaviour of abnormal cambium:- (A)Formation of rings of vascular bundles embedded in parenchymatous tissue. (B)Formation of rings of vascular bundles embedded in conjunctive tissues.

4. 1:- Abnormal Behaviour of Normal Cambium:- In many woody climbers or lianas the cambium is normal in position but its activity is abnormal and with the result anomalous structure are formed. Examples:- The stem of Cucurbita ten vascular bundles arranged in two rings of five each. Each vascular bundle is conjoint, open and bicollateral having an outer and inner cambium. The outer cambium of both inner and outer bundles becomes active along with the parenchymatous cells of the ground tissue and the combine to form a more or less wavy ring of cambium. This normal cambium behaves abnormally as it cuts off secondary xylem and phloem in vascular bundle region only, resulting in the increased size of the bundle. Cucurbita stem :- (A) The cambium forms vascular tissues only in the region of vascular bundle.

5. TS in Cucurbita stem

6. (B) The cambium forms usually large proportion vascular tissues only in the region of vascular bundle . Bignonia stem:- The young stem shows a wavy outline with prominent ridges and furrows. At the start of secondary growth, the fascicular and interfascicular cambium become active and join to form a cambium ring. This cambium ring behaves "normally in the beginning, giving more secondary xylem towards inner side and less secondary phloem on outer side. However, after sometime the cambium ring develops unidirectional areas of cambium at four diagonal points. Hence at these four points lesser amounts of xylem are cut off internally, whereas massive amounts of secondary phloem are cut off externally. These phloem masses intrude inwards forming four deep wedges of irregular width and supported by transverse bands of sclerotic cells.

7. TS in Bignonia stem

8. TS in Bignonia stem

9. 3. The cambium forms irregular patches of parenchyma in xylem :- Urtica dioica stem : The young stem of U. dioica shows a typical dicotyledonous structure having a ring of conjoint, open and collateral vascular bundles . At an early stage, a normal cambial ring is formed which behaves Normally cutting off secondary xylem towards inner side and secondary phloem towards outer side . However, after sometime the cambium begins to behave abnormally at certain places only, cutting off parenchymatous cells on the inner side, instead of secondary xylem . After cutting off a group of parenchymatous cells, the cambium again begins to behave normally and resumes its normal activity, forming secondary xylem above the parenchymatous group. The process sis repeated again and again, resulting in the formation Of islands of parenchyma which are embedded in the secondary xylem or wood.

10. TS in Urtica stem showing alternative bands of 2ry xylem and parenchymatous bands (Parenchyma islands Parenchyma band (Parenchyma islands) 2ry xylem band

11. 2:- Abnormal cambium showing abnormal activity A new cambium ring or accessory cambium arises from the cortex or pericycle. The cambial ring being placed abnormally functions in an abnormal manner . The stem has a typical dicotyledonous structure. Extra- stelar cambium originates from the cells of the inner cortex or the pericycle. It forms secondary xylem and secondary phloem. A ring of conjoint, collateral vascular bundles is thus formed, separated by parenchymatous cells. The first cambium ceases its function after forming the ring of vascular bundles. Mirabilis stem:- (A) Formation of rings of vascular bundles embedded in parenchymatous tissue .

12. The last cambial ring cuts off sclerenchyma alternating with secondary xylem on the inner side and secondary phloem and parenchyma on the outer side. Hence the last ring of vascular bundles are embedded in lignified tissue and provide mechanical strength to the stem. TS in Mirabilis stem Successive rings of accessory cambia are formed, from the secondary parenchyma, behave in a manner similar to the first one

13. Sclerenchyma at the outermost ring of VB

14. (B) Formation of rings of vascular bundles embedded in conjunctive tissues. The cambial ring originates in the conjunctive tissue and gives off secondary xylem tissue on the inner side and secondary phloem tissue outside. The vascular bundles appear to be embedded in a mass of conjunctive tissue, e.g. Bougainvillea, Boerhaavia etc. The first cambial ring is extra- stelar in origin and arise from the pericycle, followed by successive rings of cambia. The cambial ring cuts off secondary xylem alternating with secondary parenchyma on the inner side and secondary phloem above secondary xylem. The cells of the secondary parenchyma are fusiform, more or less radially arranged and usually develop lignified, thickened walls. These are referred to as conjunctive tissue or ground tissue. Bougainvillea stem:-

15. In some species of Bougainvillea, the conjunctive tissue consists entirely of sclerenchyma and cannot be demarcated from the xylem of the embedded vascular bundles, hence the secondary phloem appears in the form of islands or isolated groups apparently surrounded by conjunctive tissue. They should not be mistaken as included phloem. Successive rings of cambia are which behave in a manner similar to the first ring, as a result, concentric layers armed of vascular bundles are formed embedded in conjunctive tissue . Successive rings of cambia are formed which behave in a manner similar to the first ring, as a result, concentric layers of vascular bundles are formed embedded in conjunctive tissue .

16. TS in Bougainvillea stem

17. TS in Bougainvillea stem

18. This micrograph shows the beginning of secondary growth within the Bougainvillea stem . Note the cambial zone ( CZ) immediately beneath the starch sheath ( SS ), and the central part of the stem which is occupied by primary bundles, within which secondary growth is occurring. The internal vascular bundles are associated with conjunctive tissue . The primary bundle (encircled) has been formed by the vascular cambium.

19. Detail, showing several included vascular bundles. The vascular cambia produce vessels, axial parenchyma and sometimes fibres to the inside and indefinite amounts of secondary phloem to the outside in these included bundles Details of the anomalous growth which occurs in Bougainvillea Note the included vascular bundles (white ovoids ), embedded

20. The vascular bundles are arranged in three rings (anomalous structure, two large centrally placed in medulla, middle ring of 6-14 loosely arranged bundles and an outer ring of small 15-20 bundles. The three rings of bundles originate from the procambial strands. Secondary growth in the two medullary bundles and in the bundles of the middle ring is limited, resulting in slight increase in size only The intra- fascicular cambium of these bundles function normally, forming secondary xylem on the inner side and secondary phloem on the outer side, and as secondary growth progresses, the primary phloem gets . crushed, forming a cap like structure of dead cells over the newly formed phloem. Boerhaavia:- However, most of the secondary growth of the stem takes place from the cambial activity of the outer ring of bundles. The intra-fascicular and interfascicular cambium join to form a cambium ring.

21. Maheswari (1930) observed that the ring forms secondary xylem in the intrafascicular region and lignified, conjunctive tissue in the interfascicular region on the inner side, and secondary phloem above. The secondary xylem and parenchyma opposite to conjunctive tissue, on the . outer side. After the formation of secondary tissue, the cambium. ceases its activity and a new cambium ring arises by the joining of secondary parenchyma cells, opposite to the conjunctive tissue, and the pericycle

22. TS in Boerhaavia stem

23. Cross section of Boerhaavia stem, showing successive rings of xylem and phloem

24. TS in Boerhaavia stem