Anatomy of the vascular cambium of Acacia nilotica (L.) Del. var. telia Troup (Mimosaceae) in relation to age and season

the majority of fusiform initials are multinucleate, a few having as many as eight nuclei. Their length increases down the stem from the apex, attaining a maximum in the old trunk and declining slightly near the base. The width of the initials exhibits similar variation. In the main trunk, fusiform initials, relatively short at the time of cambial reactivation (April), elongate steadily until July. There is a sharp decline in August/September, the cell length recovering during the winter. Seasonal variation in cell width is inconsistent. Ray cell initials, on the other hand, do not vary much in size. They divide more frequently in the older stem, adding to the size of rays. In young shoots, short and uni- to biseriate rays are most abundant, whereas tall and multiseriate rays dominate the cambial surface in the trunk region throughout the year, with their minimum population in the early phase of cambial activity and the maximum during peak activity. The overall proportion of fusiform initials in the cambial cylinder initially increases with age, from young shoots towards the base, and later becomes more or less constant in the trunk region. Here it remains noticeably high during the active growth period and relatively low for the rest of the year.