Question

Plants having little or no secondary growth are
(A) Conifers
(B) Grasses
(С) Cycads
(D) Deciduous angiosperms

Answer 1

Hint: The growth of roots and stems that occurs in length with the help of apical meristems is called the primary growth whereas the growth of roots and stems in girth that is in width with the help of lateral meristems is called the secondary growth.

Complete answer: All plants undergo primary growth but apart from primary growth, most of the dicotyledonous plants exhibit secondary growth also. Generally secondary growth does not occur in monocots due to the lack of vascular cambium in them. Intrafascicular cambium, interfascicular cambium and cork cambium are the lateral meristems that participate in the secondary growth of dicots.
Now let us match this with given options:
> Conifers: they are the kind of gymnosperms . Secondary growth occurs in the stems and roots of gymnosperms also. Thus this option is not correct.
> Grasses: grasses are monocots; they can not be divided into two parts . Generally secondary growth does not occur in monocots due to the lack of vascular cambium in them. Thus this option is correct.
> Cycads: they are kind of gymnosperms . Secondary growth occurs in the stems and roots of gymnosperms also. Thus this option is not correct
> Deciduous angiosperms: The secondary tissues include secondary xylem, secondary phloem, secondary medullary rays, cork and secondary cortex. These all tissues constitute the secondary body of most dicotyledons. So secondary growth occurs in angiosperms.

Our required answer is B)grasses.

Note: As the tree continues to grow for several years and if it remains in the stage of secondary growth, the greater portion of its secondary xylem or wood turns dark brown in colour. These changes are more pronounced in the older parts of the stem. These areas are present in the central or innermost layers of the stem. These areas turn dark in colour due to progressive filling and deposition of organic compounds like tannins, resins, oils, gums, aromatic substances and essential oils in the vessels and tracheids of older secondary xylem.