FLORAL DEVELOPMENT IN SAURURUS CERNUUS (SAURURACEAE): 1. FLORAL INITIATION AND STAMEN DEVELOPMENT

The inflorescence of Saururus cernuus L. produces lateral “common” primordia in acropetal succession on the flanks of the inflorescence meristem; curiously, the “subtending” bract is initiated upon the lateral primordium rather than subtending it. On the basis of mature floral structure, flowers of S. cernuus have previously been described as having spiral initiation of parts. The current ontogenetic investigation contradicts this interpretation. Stamens arise in three successive pairs; the carpels also are initiated in pairs. Floral symmetry is shown to be bilateral from the onset of organ initiation, a rare feature among primitive angiosperms. On the basis of symmetry and paired initiation of organs, the possibility of close relationships between Saururaceae and Magnolialian or Ranalian lines appears remote.     

FLORAL INITIATION AND EARLY DEVELOPMENT IN ERIGERON PHILADELPHICUS (ASTERACEAE)

The order of floral initiation and subsequent organogeny of Erigeron philadelphicus L. (Asteraceae: Astereae) was found to deviate from the acropetal pattern generally reported for the Asteraceae. Light micrographs show periclinal divisions in the first, second, and deeper subsurface layers of cells on the flanks of the inflorescence apex as the earliest evidence of floral initiation. Scanning electron microscope micrographs indicate that the disk flowers appear first and arise as small protuberances approximately one-third of the way up the previously and undifferentiated highly convex inflorescence apex. A succession of disk flowers arises acropetally in a complex anthotaxy characterized by about 21 dextrorse and 12–15 sinistrorse parastichies (although this pattern is obscured at the apex). After one to three disk flowers have been initiated in each parastichy, the first ray flower initials can be seen to initiate in sites proximal to the oldest and largest disk flowers. Additional ray flowers then initiate basipetally following the dextrorse parastichies established by the disk flowers. Overall floral initiation on the inflorescence apex proceeds acropetally for the disk flowers and basipetally for the ray flowers until the available space is filled. Floral development adheres to the same plan—proceeding bidirectionally on the inflorescence meristem with the oldest and most complete flowers of both types located on the equator established at initiation.     

Flowering in Xanthium strumarium: INITIATION AND DEVELOPMENT OF FEMALE INFLORESCENCE AND SEX EXPRESSION

Vegetative plants of Xanthium strumarium L. grown in long days were induced to flower by exposure to one or several 16-hour dark periods. The distribution of male and female inflorescences on the flowering shoot was described, and a scoring system was designed to assess the development of the female inflorescences. The time of movement of the floral stimulus out of the induced leaf and the timing of action of high temperature were shown to be similar for both the apical male and lateral female inflorescences.     

INITIATION AND DEVELOPMENT OF ROOTS IN JUVENILE AND MATURE LEAF BUD CUTTINGS OF FICUS PUMILA L.

Adventitious root formation (ARF) was studied in woody leaf bud cuttings of Ficus pumila L., creeping fig. Juvenile cuttings rooted easily, whereas only mature cuttings treated with indole-3-butyric acid (IBA) attained any rooting success. In the rooting process, both juvenile and mature material exhibited dedifferentiation of phloem ray parenchyma, root initial formation, primordia differentiation, and root elongation. The early stages of adventitious rooting were most critical since few primordia were observed in mature controls. The stages leading up to root primordia differentiation and elongation occurred more rapidly in IBA-treated juvenile vs. mature cuttings; however, time differences in both types between first observable roots and maximum rooting were comparable. Root primordia differentiated from basal callus of some cuttings, but neither these nor the few primordia in mature controls elongated into well-developed roots. Anatomical differences between the juvenile and mature material did not account for rooting disparity, nor did presence of perivascular fibers, sclereids, and laticifers retard rooting.     

PATTERNS OF FLORAL DEVELOPMENT IN AGALINIS AND ALLIES (SCROPHULARIACEAE). II. FLORAL DEVELOPMENT OF AGALINIS DENSIFLORA

Initiation of floral primordia begins in Agalinis densiflora with production of two lateral adaxial calyx lobe primordia followed by a midadaxial primordium, and then primordia of two abaxial calyx lobes. Initiation of three abaxial corolla lobe primordia is succeeded by that of two stamen pairs and then by primordia of two adaxial corolla lobes. The primordium of the abaxial carpel appears before the adaxial one. Except for the calyx, initiation of primordia proceeds unidirectionally from the abaxial to the adaxial side of the floral apex. Zygomorphy in the calyx, corolla, and androecium is evident during initiation of primordia and is accentuated during organogenesis. The calyx undergoes comparatively rapid organogenesis, but the inner three floral series undergo a protracted period of organogenesis. The perianth series reach maturation prior to meiosis in the anthers. Maturation of the androecium and gynoecium are postmeiotic events.     

MORPHOLOGICAL STUDIES IN ZYGOPHYLLACEAE. I. THE FLORAL DEVELOPMENT AND VASCULAR ANATOMY OF NITRARIA RETUSA

The floral development and vascular anatomy of Nitraria retusa were investigated in order to understand its characteristic androecium of 15 stamens and to clarify the systematic position of the genus relative to Zygophyllaceae. Sepals arise in a helical sequence and are relatively small at maturity. Petals are initiated almost simultaneously or in a rapid helical sequence. Five stamen primordia arise opposite the sepals. Next, two other antesepalous primordia are incepted centrifugally to the first primordia on the remaining receptacular surface. The outer stamens tend to be squeezed between the petals and upper stamens and appear to make up an antepetalous whorl of stamens. Three carpels arise from a low ringwall and grow into a hairy trilocular pistil. In each locule a single pendulous ovule is present. Disclike nectarial tissue is initiated in pits between the stamens and petals. Long trichomes develop on its surface. It is concluded that the androecium is linked with a haplostemonous condition because the stamens of each triplet develop on strictly localized sectors. The distinction between stamens arising on complex primordia and the inception of three independent units is explained by the “principle of variable proportions.” The vasculature also tends to confirm that the outer stamen pairs belong to antesepalous triplets.     

BASIDIOSPOROGENESIS IN BOLETUS RUBINELLUS. I. STERIGMAL INITIATION AND EARLY SPORE DEVELOPMENT

Sterigmal initiation in Boletus rubinellus resembled hyphal tip growth. Four stages in early basidiospore development have been delineated based on gross morphology, and changes in wall layers and cytoplasm. Changes in wall layers and cytoplasm during spore development were stage-specific. During Stage 1 the spore wall consisted of two layers identical to those of the sterigmal wall with occasional pellicle remnants on the outer surface. The onset of wall differentiation began in Stage 2, and during Stage 3 wall layers characteristic of the mature spore developed. At Stage 4 there was a pronounced gradient in wall thickness from the apex to the base of the spore. Small vesicles (30–60 nm diam) were uniformly distributed in the cytoplasm of spherically enlarging spores (Stage 2), but during spore elongation (Stages 3 and 4) numerous larger vesicles as well as small vesicles aggregated at the spore apex. A variety of cytoplasmic organelles entered the spore during Stage 3; however, migration of storage materials and the nucleus to the spore did not occur until late basidiospore development. The hilar appendix body developed in the earliest spore primordium and persisted until Stage 3. Development of wall layers and their differential thickening, distribution of vesicles, and probable function of the hilar appendix body are discussed with reference to the control of spore shape. Systematic implications of the data are considered.     

油松树脂道的发生和发育研究

关于松科植物的树脂道,以往都认为是以裂生方式发生。本文通过对油松各类器官的发育解剖学研究,发现其各类器官中树脂道的结构,发生和发育方式并不完全一致,并对产生这些差异的原因进行了分析和讨论。     

CONTROL OF IN VITRO SEPAL DEVELOPMENT OF EXCISED FLORAL BUDS OF AQUILEGIA (RANUNCULACEAE)

Excised floral buds of Aquilegia formosa Fisch. were grown on a coconut-milk medium containing the minerals and vitamins of Murashige and Skoog, sucrose, and kinetin. The plant growth regulators indoleacetic acid (IAA, 0.5 mg/liter) and gibberellic acid (GA, 2.0 mg/liter) were added singly and in combinations; both were omitted from the control medium. The addition of GA to the basal medium was required to support sepal development on flowers at all phases of development. The formation of stomatal complexes in the epidermis of the sepals occurred only in the presence of GA. Sepals grown in the presence of GA also contained trichoblasts and developing trichomes, while none were formed in the absence of GA. The role of IAA in the development of these idioblasts was not clear but it appeared to have no effect. The hormones GA and IAA had different effects on the growth of the sepals. In the presence of GA the sepals increase in length until comparable with sepals grown in vivo. However, the sepals remained small when GA was omitted from the medium. Upon closer examination of this effect, it was determined that there was a direct proportionality between an increase in cell number in the epidermis and an increase in sepal length. The role of the two hormones in increasing epidermal cell length in sepals was distinct and separate. Exogenous IAA had no effect upon cell division but was required for cell elongation, while GA was required for cell division and had no effect on cell elongation. The GA effect in promoting cell division in the sepals was substantiated by use of autoradiography. If the buds were grown on media with GA, twice as many epidermal cells along the central file incorporated significant amounts of tritiated thymidine. The cell cycle of the epidermal cells of the GA-treated sepals was ca. 8.7 hr in duration and ca. 13.0 hr if GA was deleted from the medium.     

A SCANNING ELECTRON MICROSCOPIC STUDY ON THE INITIATION AND DEVELOPMENT OF FLORAL ORGANS OF BRASSICA NAPUS (CV. WESTAR)

The initiation and development of the floral organs of Brassica napus L. (cv. Westar) were examined using the scanning electron microscope. After transition of the vegetative apex into an inflorescence apex, flower primordia were initiated in a helical phyllotactic pattern. The sequence of initiation of the floral organs in a flower bud was that of sepals, stamens, petals and gynoecium. Of the four sepal primordia, the abaxial was initiated first, followed by the two lateral and finally the adaxial primordium. The four long stamens were initiated simultaneously in positions alternating with the sepals. The two short stamens were initiated basipetal to and outside the long stamens, and opposite the lateral sepals. The petals arose on either side of the two short stamens and the gynoecium was produced from the remainder of the apex. During development, the sepal primordia curved sharply at the tips and tightly enclosed the other organs. Stamen primordia developed tetralobed anthers at an early stage while filament elongation occurred just prior to anthesis. A unique pattern of bulbous cells was present on the abaxial surface of the anther. Growth of petal primordia lagged relative to the other floral organs but expansion was rapid prior to anthesis. The gynoecium primordium was characterized by an invagination early in development. At maturity, there was differentiation of a papillate stigma, an elongated style and a long ovary marked externally by sutures and divided internally by a septum. Distinct patterns of cuticular thickenings were observed on the abaxial and adaxial surfaces of the petals and stamens and on the surface of the style. The patterns were less obvious on the sepals and ovary. Stomata were present on both surfaces of the mature sepals, on the style and restricted areas on the abaxial surface of the anthers and nectaries but were absent from the petals, the adaxial surface of the stamens and the ovary. No hairs were present on any of the floral organs.     

INFLORESCENCE AND FLOWER DEVELOPMENT IN THE PIPERACEAE III. FLORAL ONTOGENY OF PIPER

Floral development in Piper was compared between four-staminate species (P. aduncum and P. marginatum) and six-staminate species (P. amalago). All Piper species have a syncarpous gynoecium composed of three or four carpels. The floral apex is initiated by a periclinal division in the subsurface layer in the axil of a bract 40-55 μm high; initiation of the bracts occurs separately and considerably earlier. The floral primordium widens and the first pair of stamens are initiated at either side. The median anterior stamen forms next, and the median posterior later. This sequence is common to all species studied. In the six-staminate P. amalago, the last two stamens form simultaneously in lateral-anterior positions. The stamens hence arise as pairs, and symmetry is bilateral or dorsiventral. The three or four carpels arise simultaneously; they are soon elevated on a gynoecial ring by growth of the receptacle below the level of attachment of the carpels to produce a syncarpous gynoecium. The floral apex lastly produces the solitary basal ovule and is used up in its formation.     

THE FLORAL AND EXTRA-FLORAL NECTARIES OF PASSIFLORA. I. THE FLORAL NECTARY

Floral nectary development and nectar secretion in three species of Passiflora were investigated with light and electron microscopy. The nectary ring results from the activity of an intercalary meristem. Increased starch deposition in the amyloplasts of the secretory cells parallels maturation of the nectary phloem. Large membrane-bound protein bodies are observed consistently in phloem parenchyma cells, but their function is presently unknown. The stored starch serves as the main source of nectar sugars at anthesis. Plastid envelope integrity is maintained during starch degradation, and there is no evidence of participation of endoplasmic reticulum or Golgi in the secretion of pre-nectar. It is concluded that in these starchy nectaries granulocrine secretion, commonly reported for floral nectaries, does not occur.     

DEVELOPMENTAL ANATOMY IN ROOTS OF IPOMOEA PURPUREA. II. INITIATION AND DEVELOPMENT OF SECONDARY ROOTS

In seedlings of Ipomoea purpurea secondary roots are initiated in the primary root pericycle opposite immature protoxylem. Cells derived from immature endodermis, pericycle, and incipient protoxylem and stelar parenchyma contribute to the primordium. The derivatives of the endodermis become a uniseriate covering over the tip and flanks of the primordium and emerged secondary root; the endodermal covering is sloughed off when the lateral root reaches 1–5 mm in length. A series of periclinal and anticlinal divisions in the pericycle and its derivatives gives rise to the main body of the secondary root. The initials for the vascular cylinder, cortex, and rootcap-epidermis complex are established very early during primordium enlargement. After emergence from the primary root, the cortical initials undergo significant structural modifications related to enlargement of the ground meristem and cortex, and the rootcapepidermal initials are partitioned into columellar initials and lateral rootcapepidermal initials. Procambium diameter increases by periclinal divisions in peripheral sectors. The mature vascular cylinder is comprised of several vascular patterns, ranging from diarch to pentarch, that are probably related ontogenetically. Cells derived from incipient protoxylem and stelar parenchyma cells of the primary root form the vascuar connection between primary and secondary roots.     

DEVELOPMENT OF TRISTYLY IN PONTEDERIA CORDATA (PONTEDERIACEAE). I. MATURE FLORAL STRUCTURE AND PATTERNS OF RELATIVE GROWTH OF REPRODUCTIVE ORGANS

Pontederia cordata is a tristylous, self-incompatible emergent aquatic. Measurements of reproductive organs in mature flowers and developing buds and analysis of relative growth rates of the styles, filaments, and floral tube were used to analyze the developmental processes that result in reciprocal positioning of reproductive parts among the style morphs. Flowers are trimerous with two series of three tepals, two series of three stamens, and a tricarpellate ovary with a single ovule. Each flower has stamens of two lengths, but the two lengths correspond to upper vs. lower position in the zygomorphic flowers, not to the two series initiated in the primordium. Morph-dependent variation in stigma height depends on differences in style length, not ovary length. Differences among morphs in anther height result from differences in the position of filament insertion on the floral tube and differences in filament length. Styles of the three morphs develop to different lengths as a result of two distinct processes. Styles of L and M morphs develop at different rates with the L style growing more rapidly than the M style, whereas styles of the S morph have a brief period of rapid growth followed by early inhibition. Stamen growth in the S morph also differs qualitatively from that in the L and M morphs, which are distinguished from each other by quantitative differences in growth rates. Results indicate that the developmental processes that result in the complementary arrangements of organs in different morphs are morph-specific. An attempt is made to integrate the findings of this study with the model for genetic control of tristyly.