Root sclereids ofSyzygium cumini (L.) Skeels

Abstract

Sclereids in the roots ofSyzygium cumini (L.) Skeels (Myrtaceae) are polymorphic. In addition to the brachy-, osteo- and bizarre sclereids, there occur an interesting kind of sclereids—the fibre sclereids—resembling the fibres in some respects.

Sclereids appear only after the onset of secondary activity and fall into one of the following categories depending on their origin: (a) a continuous strand of sclereids in the secondary cortex. This develops from parenchymatous initials that are derivatives of phellogen. Fibre sclereids occur only in this region along with ordinary sclereids and a few fibres. (b) sclereids formed through secondary sclerosis of distal mature parenchyma cells of the dilating phloem rays. (c) Sclereids formed through secondary sclerosis of mature parenchyma cells in old phloem. Sclereids of categoriesb andc a but on those ofa forming a composite strand.

All the kinds of sclereids here possess thick, highly lamellated lignified walls with simple and wide pit canals ending in round or oval apertures. The adult sclereids are devoid of nuclei, starch or crystals. Insoluble tannin is present in them except in those formed from phloem parenchyma.

Ontogenetical stages of the various kinds of sclereids are similar except that fibre sclereids show a pronounced intrusive growth which although initially bipolar later becomes unipolar. Other kinds of sclereids show either a purely symplastic growth or a combination of various degrees of symplastic and intrusive growth which is either diffuse (some osteosclereids) or multipolar (bizarre sclereids).

The inadequacy and unreliability of the existing classifications of and criteria for classifying different mechanical elements particularly in sclereid containing plants are discussed and suggestions made.