Simon J. Owens

Taxonomic and functional implications of stigma morphology in species ofCassia, Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.

The genetic control of self-incompatibility in the genus Gasteria (Liliaceae)

SummaryThe results of intercrossing 11 fertile F1 individuals obtained from an interspecific cross between two self-incompatible species of Gasteria, viz. G. liliputana and G. humilis, reveal that at least two genes control the self-incompatibility reaction. The site of pollen tube inhibition in incompatible matings is confirmed as the ovule.

Embryology and breeding systems inCrocus (Iridaceae)—a study in causes of chromosome variation

A detailed description of female reproductive structures inCrocus is given, using three different techniques: wax embedding and sectioning, SEM, and observation of cleared ovules by interference contrast microscopy. The results of this examination, and a chromosomal investigation of the intraspecific hybrids obtained by crossing specimens ofC. speciosus of different karyotypes, are used to test the hypothesis thatCrocus is apomictic. Although facultative diplospory cannot be entirely ruled out, it is suggested that apomixis is an unlikely explanation from the unusual amount of chromosomal variation found in some species ofCrocus, and alternative causes are discussed.

Self-incompatibility and the pollen-stigma interaction inTradescantia ohiensis rafin

SummarySelf-incompatibility (SI) is reported for an accession ofTradescantia ohiensis. Pollen tube inhibition is stigmatic. The stigma is wet and papillate, the papillr surface bearing conspicuous blebs particularly in the mid- and basal regions of the cell. A proteinaceous pellicle is present on the surface of the papillar cuticle. The penetration of the stains calcofluor white and alcian blue into the cell wall of fresh stigma papillae strongly indicates that the permeability of the papillae is greatest at the mid-region of the cell and not at the tip. When single pollen grains are attached to the tip of a papilla there is either no response at all or the pollen adheres to the papilla. When attached in the mid-region pollen adheres, and often germinates. It is concluded that the sites of pollen receptivity are the mid- and basal regions of the papular cell.

A light and electron microscopic study of stigmas inAneilema andCommelina species (Commelinaceae)

SummaryThe stigmas of species inAneilema andCommelina are trifid and comprise elongate papillae. Progressive degeneration of papular cells is observed in stigmas from open flowers and at anthesis papillae may be moribund and collapsed. Fluid emanating from the hollow style flows onto the surface through ruptures in the cuticle at the interpapillar junctions into the interstices at maturity. This secretion stains positively for protein. Stigmas are of the “wet” type.The cuticle overlying the papillar cells is ridged and at the final stages prior to flowering this cuticle becomes detached from the underlying cellulosic wall. The sub-cuticular space so formed is filled with secretion. InAneilema species detachment of cuticle is at the papillar tip and along the lateral walls. InCommelina species the anticlinal walls of adjacent papillae are strongly attached for much of their length and thus detachment of cuticle is restricted to the papillar tip. The cell wall at the tip in both genera may proliferate forming a rudimentary transfer-cell type wall. The secretion is considered to be produced by the papillar cells. It is PAS positive but fails to stain for protein and in both the light and electron microscopes appears heterogenous.Pollen attachment, hydration, germination and early tube growth are very rapid following self-pollination, the pollen tubes entering the neck of the style within ten minutes of attachment.A unique character combination involving pollen and stigmas in these genera indicates a monophyletic origin.

Incompatibility studies in the genus Gibasis section Heterobasis D. R. Hunt (Commelinaceae)

SummaryTwo species in the genus Gibasis section Heterobasis have been examined to confirm their incompatibility reaction and to determine its genetic control. Five individuals of G. oaxacana (2x=16) from a single Mexican population (Hunt 8175) were found to be self-incompatible. Three accessions of tetraploid cytotypes (4x=32; Hunt 7012, 7072 and 7160) and two accessions of hexaploid cytotypes (6x=48; Jones 72 and Bacigallipo 711257) of Gibasis geniculata were found to be self-compatible. Analysis of an F1 population raised from an intercross between two heterozygous genotypes of G. oaxacana was consistent with an hypothesis that self-incompatibility is controlled by a single multiallelic gene acting gametophytically in the pollen.Unilateral incompatibility was found in crosses between G. oaxacana and G. geniculata.

The components of the sexual reproduction process and the pathway to in Vivo fertilization in higher plants

Summary Successful higher plant reproduction depends upon the development of functional reproductive structures and viable gametes in the flowers, transfer of viable pollen onto a receptive and compatible stigma, pollen germination, directed pollen tube growth to the ovule, gamete delivery and nuclear fusion. In higher plants, two nuclear fusions must take place — one sperm nucleus fusing with the egg nucleus to form the zygote, the other sperm fusing with the polar nuclei to form the endosperm. Seed development to maturity may follow.