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Anomalous secondary growth due to abnormal activity of cambium

Anomalous secondary growth due to abnormal activity of cambium

 Anomalous secondary growth is an abnormal type of secondary growth. It is the result of deviation in the cambial activity from the normal type found in most of the dicots.

 This type of anomaly is generally found in woody climbers (lianas) and the main purpose of abnormal behavior of cambium is to produce less xylem to make the plant more flexible to climb to its support without breaking.

Cambium functions in the following ways- 

(i) Formation of fissured xylem as seen in Tinospora stem 

  • In the stems of Tinospora, the cambium produces the vascular tissues i.e. xylem and phloem only in the intra-fascicular region whereas in the inter-fascicular region paranchymatouc tissues are produced. Thus, the vascular bundles remain discrete, separated by paranchymatous tissues.
  • In addition, even the intra-fascicular cambium at certain spots produces paranchymatous secondary medullary rays both towards the inside and outside. Thus, in the old stems, the xylem becomes fissured due to development of paranchymatous secondary medullary ray.

 (ii) Formation of phloem wedge as seen in Bignonia stem

 

  • In the stems of Bignonia, the origin, position, and function of cambium ring is normal in the initial stages of growth producing large amount of secondary xylem towards inner side and small amount of secondary phloem towards outer side.
  • In later stages of secondary growth, at some places (usually at four places in crosswise planes) the cambium starts cutting off more amount of secondary phloem towards the outer side and less amount of secondary xylem towards the inner side.
  • These phloem patches later get embedded deeply into the secondary xylem.
  • This results in the formation of four deep wedges of secondary phloem in the secondary xylem region and a ridged and furrowed xylem cylinder is produced.
  • The phloem patch is traversed by sclerenchyma bars which gives mechanical support to thin-walled phloem tissues.
  • The cambium is situated on the inside of the furrows and on the outside of the ridges, while the radial surface is occupied by paranchymatous medullary ray tissues.

(iii) In some other cases, the cambium activity is restricted to certain segments only where it cuts off cells actively while at other segments it is almost inactive or show limited activity, resulting in the formation of ridged stem (eg. Bauhinia rubiginosa). In Bauhinia blumenaviana, the cambial activity is restricted at two opposite side only and consequently a flattened strap like stem is produced.

https://content.patnawomenscollege.in/botany/Bot-CC-305%28Anomalous%20secondary%20growth%29.pdf

(iv) In yet some other cases like in the stem of Doxantha, furrows of secondary phloem are present in the cylinder of secondary xylem. It is due to the development of unidirectional and bidirectional arcs of cambium. Unidirectional arc of cambium produces little or no secondary xylem but extensive amount of secondary phloem, whereas the bidirectional arc of cambium produces as much or more secondary xylem than secondary phloem. Subsequently, four or more furrows of phloem are formed which act as shock absorber.

Author Name: Dr Pinky Prasad

Department: Botany

Email id: pinky.bot@patnawomenscollege.in