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Primary Tracheary Elements of the Genus Oryza
Dissertation Abstract:
The structure of lateral wall and overlap areas of xylem elements in the leaf, stem and root of 21 species of Oryza was studied.
The predominant type found in all plant organs was the reticulate. The second-order thickenings were represented by oblique strands, strand ontogenically modified into sheets, and rarely, sheets.Pitted elements were commonly found in roots and seldom in leaves and stems. Almost all had oval to circular-bordered pits with oval, rectangular to circular inner apertures.
The preodominant type of perforate overlap was the simply perforate plate. Transitional perforation plates represented intermediate forms between the simple and scalariform ones. The simple perforation plate was shown to be usually derived from the combined breaking and fusion of bars, and rarely from either breaking or fusion alone.
Evolutionary relationships between and among Oryza species could be obtained from types of perforation plates in later-formed elements in roots and leaves, and from types of lateral wall. On the basis of the first criterion, the following may be concluded: (a) closely related species are O. sativa and O. perrieri, and another group O. grandiglumis and O. ridleyi, with the former group being more advanced; (b) O. eichingeri, O. minuta, O. malampuzhaensis and O. longiglumis may have been derived from O. officinalis or share an immediate common ancestor; (c) O. australiensis is intermediate between O. sativa complex and O. officinalis; and (d) O. coarctata is unique and may well be removed from the genus. On the basis of type of lateral wall, O. latifolia can be separated from O. sativa var. coilina and O. officinalis, and O. barthii from O. perennis on account of the absence of the earliest-formed element in the first species of each of these groups.
