Production of stigma exudate per flower of Petunia hybrida is about 200 μg. The effect of light, temperature, metabolic poison and emasculation on the production of the exudate at different ages of the bud has been studied. The presence of a thin film of water below the stigmatic exudate has been demonstrated. Physical properties of the exudate such as relative viscosity and surface tension have also been determined. Chemical analysis of the stigmatic fluid showed that it consists primarily of an oil, sugars and amino acids. No protein could be detected. It also contains no acid phosphatase.Behaviour of the pollen from its deposition on the stigmatic fluid until it germinates on the stigma surface has been studied in vivo and also with the aid of an "artificial stigma".The role of the stigmatic fluid in pollination has been determined.

A mature stigma of Petunia hybrida ready for pollination shows 4-6 large shining drops of the exudate along with numerous smaller ones. A developing style and stigma have a columnar tissue that flares at the top. In the stigma there can be distinguished a secretory and a storage zone. In the former, schizogenous cavities are formed which are filled with the exudate. The mode of formation and secretion of the drop has been studied with light and electron microscope. The nature of reserves has been studied histochemically.The exudation takes place in two stages. In the first stage, the epidermal and papillae cells release out the oily exudate upon rupture of the cuticle. The second phase of exudation begins with anthesis. The exudate from the schizogenous cavities is released between the epidermal cells. There are distinct loci on the stigma surface where more exudate is given out than at other places.

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IDRésumé. -Les cultures de cals de /lanunculus sceleratus donnent naissance it un grand nombre d'embryoïdes qui gernwnt in situ ou lorsqu'ils sont st'•parés el transférés sur un milieu frais. Les pl'tites plantt•s t~n résultant, forment ulléricurcmt•nt des cmbryoïdes à partir de ecllult•s individuelles situées dans ]'{•pidermc de l'hypocotylc.Des études au microscope électronique ont montr.:, des similitudes entre les t•<•llult•s cmbryogènes des cals et celles des tiges de petites plantes pron•nant de l'(,piderme en matière de taille des cellules, taille du noyau, degré de vacuolisation, abondance des ribosomes et des mitnchondrit•s, présence d'arnyloplastes et prt:,dominance de sphérosomes. Elles ont rnontr(-ullt-ricuremt•rlt que la discontinuité protoplasmique entre les cellules emb1•yogènes et les n•llules non impliquét•s directt•mt•nt dans l'embryogt>nèse, m• pré,cé•dait pas l'initiation du développement de l'embryoïde.Des embryoïdes semblent provenir dans quelques cas, de cellules individuellt•s à la surface d'aggrt-gats des cals, mais il n'est pas certain que tous ont pour origine une cellule individuelle. Les cl'llules intt•rnes des aggr<;gats dt> cals t•ontiennent des structures mitochondriales extrêmement allongées, suivant le contour du noyau, et l'on pense que cela suggère, soit que ces structures sont formées ti la suite de la fusion de mitochondries, soit que ce sont ct•s structures qui donnent naissance à des mitochondries.

Morphogenesis of floral buds excised at various stages of development was followed in vitro. The buds comprising the primordia of sepals and stamens (Stage I) failed to complete normal development on any of the nutrient media tried. However, the initiation and further development of carpels occurred even on a medium containing mineral elements, glycine,vitamins and sucrose. On the other hand, the buds having the anthers at the pollen mother cell stage (Stage II) completed microsporogenesis and 2-celled pollen grains were formed in the anthers. The torus i.e. the central dome bearing the carpels, of Stage II, and III (buds having anthers at pollen grain stage) elongated enormously and emerged through the folded sepals. Regeneration of roots and shoot buds (especiallyin Stage II & III buds) was common.In addition, the floral buds of all stages formed callus which subsequently differentiated roots, shoot buds and embryoids leading to the formation of plantlets. The latter, in turn, developed embryoids from the epidermal and pith cells of the stem. On subculturing, the hypocotyl portion of the in vitro plantlet was capable of developing embryoids directly from the epidermal cells, whereas the radicular and plumular portions of the same plantlet first formed callus and subsequently embryoids.The growth of callus and the differentiation of embryoids could be maintained through repeated subculturing. Embryoids could be induced even on a simple medium having only mineral elements and sucrose. Among the several growth adjuvants used, a combination of coconut milk and IAA supported best callus growth and normal embryoid differentiation.

Variations in extractable cellulase and pectinase were followed during development of Hemerocallis (day lily) flowers. A peak in cellulase activity occurs in the pistil just prior to anthesis, followed by a 62% diminution in the enzyme activity at the time of anthesis. Cellulase activity, per mg protein, is about twice as high in the upper (stigma) portion as in the middle and lower one-third of the pistil tissues. No pectinase activity was detected in the pistil at all stages of development. Extractable pectinase is present at a maximum level in the very young ovary; it decreases rapidly as the ovary develops. Cellulase remains at a moderate level of activity throughout the development of the ovary, except for an increase of about 50% at pollination. Soluble cellulase and pectinase are found in mature pollen. The changes in the cell-wall hydrolytic enzymes in the pistil were pollen-tube growth. It may also promote changes in the cell walls of the pistil cells, although metabolism of the middle lamella during pollen germination is primarily controlled by pollen pectinases.

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