The course of development of the glandular and non-glandular hairs of Avicennia marina was found to be the same up to the three-celled stage. The further cell divisions of the two types of developing hairs differed in their orientation. In the non-glandular hair the cells continued to divide transversely, whereas in the glandular hair the uppermost of the three cells divided longitudinally.
In the mature hairs of both types, the peripheral wall of the cell just above the basal cell was heavily cutinized. The existence of narrow canals in the cuticle of the secretory cells of the glandular hairs was confirmed. The homology of the glandular and non-glandular hairs is discussed and it is concluded that the two types are phylogenetically related.