Annual growth rings are formed due to the activity of A. Extra-stelar cambium B. Intra-stelar cambium C. Inter-stelar cambium D. All of the above
Hint: Growth ring is a characteristic of woody trees. They can be seen in a cross-section of the stem in woody plants. It varies according to seasonal changes and can be differentiated morphologically. The cambial activity gives rise to the formation of annual growth rings.
Complete answer: Intrafascicular cambium is a meristematic tissue, located between the xylem and the phloem in dicotyledonous plants. The pith rays, situated at the edges of the intrafascicular cambium, undergo repeated division to form a new strip of cambium between the two vascular bundles namely, the interfascicular cambium. This entire structure including both the inter and intrafascicular cambium is collectively termed as the vascular cambium. The activity of vascular cambium produces annual growth rings in woody plants. The vascular cambial ring divides forming the secondary xylem towards the inner side and secondary phloem towards the outer side. Since the vascular cambium is present within the stele, therefore it is also termed as intra-Stelar cambium.
Additional information: The vascular cambium and cork cambium are secondary meristems that are formed in roots and stems after the tissues of the primary plant body have differentiated. The vascular cambium is responsible for increasing the diameter of stems and roots and for producing woody tissue. The cork cambium produces some part of the bark.
So, the correct answer is option B. Intra-Stelar cambium.
Note: Depending on the season, the cambial activity rate changes and there is an alternative production of narrow and wide rings in the stem. The darker wood is generally formed during summers whereas the lighter shade ring forms in the winter season.