Abstract
This study on radial growth in the stem of Citrus was carried out with an aim to notice the behavior of vascular cambium with respect to climatic and age effects. The fusiform initials vary in length from 137 to 363 μm in C. limon, 100 to 463 μm in C. paradisi, 137 to 413 μm in C. reticulata var. kinnow, and 137 to 375 μm in C. sinensis. The length rises with age, followed by decline and then again increase in C. limon. In C. paradisi, there is increase up to maximum and after decline is soon followed by constancy. In C. reticulata var. kinnow, increase in length from top to base in C. sinensis, increase up to maximum followed by a decline. Swelling of cambial cells occurs in the third week of March in C. limon, last week of March in C. paradisi, third week of April in C. reticulata var. kinnow, and second week of April in C. sinensis. The cambium turns dormant in early October in C. limon, late December in C. paradisi, early December in C. reticulata var. kinnow, and early November in C. sinensis. Thus, the cambium remains active for about 6 months in C. limon and C. sinensis, 9 months in C. paradisi, and 7 months in C. reticulata var. kinnow.
Highlights
In most dicotyledons and gymnosperms, a layer of procambial cells between the primary phloem and primary xylem matures into fascicular cambium, while the cells of pith or medullary rays which lie in between the edges of the fascicular cambium divide to form a new layer of cambium across the medullary rays, known as interfascicular cambium, resulting in the formation of a complete ring of cambium
A maximum of 23% has been observed in C. paradisi and C. reticulata var. kinnow and minimum of 18% in C. limon, whereas in C. sinensis, the ray initials constitute about 22% of tangential area of cambial cylinder in adult trees [30–34]
A similar analysis of the ray initials of the investigated species (Table 2) shows a slight initial increase from 12.44/9.86 to 15.98/13.80 μm which is followed by constancy in anticlinal and periclinal diameters of C. limon as has already been reported by Khan [10] in Terminalia arjuna and slight increase from 8.97/7.82 to 11.96/ 10.13 μm with the increasing diameter of axis in C. reticulata var. kinnow which coincides with the findings of Khan [10] in Jacaranda mimosifolia, whereas a slight initial increase followed by a decrease in the basal region is seen in anticlinal diameter of C. sinensis as has been reported by Khan [10] in Pterospermum acerifolium
Summary
In most dicotyledons and gymnosperms, a layer of procambial cells between the primary phloem and primary xylem matures into fascicular cambium, while the cells of pith or medullary rays which lie in between the edges of the fascicular cambium divide to form a new layer of cambium across the medullary rays, known as interfascicular cambium, resulting in the formation of a complete ring of cambium. A new lateral meristem, the vascular cambium, which is responsible for the “growth in thickness by the formation of secondary vascular tissues (radial growth),” is formed and adds secondary phloem toward the outer side and secondary xylem toward the inner side
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