Dehiscence Zone Research Articles

Preliminary studies on the effects of 4-chlorophenoxyacetic acid on the senescence and dehiscence of pods in oil seed rape (Brassica napus L.)

The auxin 4-chlorophenoxyacetic acid (4-CPA) has been found to delay the maturation and dehiscence of the pods of oil seed rape. Dipping pods in solutions of 500 μgl−1, 4-CPA, 36 and 39 days after anthesis delayed significantly the autolysis of the thin-walled parenchyma of the dehiscence zones, the senescence of the pod walls and the loss of water from the pod walls and seeds. Increases in both the fresh and dry weights of both pod walls and seeds were recorded in the treated pods as compared with controls.

Sem Studies on Operculum Structure in the Myxomycete Trichia crateriformis

Scanning electron microscope studies have been conducted on the operculum of sporangia of Trichia crateriformis and its structure has been compared with that of other operculate Myxomycetes. The operculum of T. crateriformis consists of a single layer of spore-like bodies that have cell walls ornamented with warty excresences similar to those of the spores. It adjoins the membranous peridium of the sporangium in a transition region which constitutes the dehiscence zone. In other taxa with operculate sporophores examined the operculum is membranous and has a structure generally similar to that of its associated peridium. The type of operculum in T. crateriformis may be unique for the Myxomycetes.

SEM Studies on Operculum Structure in the Myxomycete Trichia Crateriformis

Scanning electron microscope studies have been conducted on the operculum of sporangia of Trichia crateriformis and its structure has been compared with that of other operculate Myxomycetes. The operculum of T. crateriformis consists of a single layer of sporelike bodies that have cell walls ornamented with warty excresences similar to those of the spores. It adjoins the membranous peridium of the sporangium in a transition region which constitutes the dehiscence zone. In other taxa with operculate sporophores examined the operculum is membranous and has a structure generally similar to that of its associated peridium. The type of operculum in T. crateriformis may be unique for the Myxomycetes. Several species of Myxomycetes form sporangia furnished with a well-defined operculum. Species exhibiting this characteristic are Metatrichia vesparium (Batsch) Nann-Brem., certain species of Craterium and Licea, Perichaena depressa Libert, and Trichia crateriformis Martin. During the course of some scanning electron microscope (SEM) studies of types of authenticated specimens of taxa in the Trichiaceae, we observed that the operculum of the sporangium of T. crateriformis is strikingly different in structure from that of its contiguous peridial wall. The T. crateriformis operculum was noted to consist of discrete spore-like units with ornamented wall surfaces similar to those of the spores. A report on this apparently unique type of operculum structure is presented in this communication.

Asci of the Pezizales. VII. The apical apparatus of Galiella rufa and Sarcosoma globosum: reevaluation of the suboperculate ascus

Light and electron microscopic examinations were made on asci of Galiella rufa and Sarcosoma globosum with emphasis on the development, cytochemistry, and morphology of the apical apparatus. Comparative analysis of the fresh and revived states of the apical apparatus in G. rufa demonstrated no apparent change in wall layering and only minor differences in staining reaction with silver methenamine. Ascal tips of both species were slightly thinner walled than the rest of the ascus and possessed bistratified outer layers. The external stratum of the outer layer was more pronounced and electron dense at the apex in S. globosum. Opercula were distinguished by a cytochemically localized zone of dehiscence in G. rufa and a differential staining of the internal stratum of the outer layer in S. globosum. The ascus tips of G. rufa and S. globosum were most similar to other members of the Sarcosomataceae. The apical apparatuses of the Sarcoscyphaceae differed substantially from those of the Sarcosomataceae and the rest of the Pezizales, constituting a separate type.

Serrulacaulis furcatus gen. sp. nov., a New zosterophyll from the lower upper devonian of New York state

A new zosterophyll is described from the lower Upper Devonian of New York. Serrulacaulis furcatus is characterized by two rows of emergences which are opposite in arrangement and attached on opposite margins of the axis. They are deltoid in side view and are contiguous vertically, giving the stem a scalloped or saw-toothed appearance. Epidermis over much of the plant consists of elongate cells and interspersed isodiametric cells. The vascular strand consists of spirally thickened tracheids. Rhizomes are densely covered by rhizoids that are more numerous on small papillae and at the apex of tooth-like emergences. Aerial axes terminate in circinate apices. Some axes bear short-stalked, reniform sporangia arranged alternately in two rows on one side of the axis only. The dehiscence zone is a thickened rim over the distal, convex margin of the sporangium. Dehiscence is basipetal, producing two equal valves. Spores are smooth to slightly granulate, circular to subtriangular, with a trilete mark that extends 1 3 – 1 2 the radius and is surrounded by a darkened triangular area. Sawdonia ornata, described earlier from the same quarry, and now Serrulacaulis, are the two genera of zosterophylls proven to occur in Late Devonian time. The world-wide distribution of zosterophylls and the fact that the group is a natural one are reviewed.

BOTRYOPTERIS PINNULES WITH ABAXIAL SPORANGIA

Small sporangia borne abaxially on pinnules attached to Botryopteris foliar members are described from coal ball petrifactions of Early Pennsylvanian age. This is the first report of laminar sporangia in this genus. Sporangia are stalked and borne singly near lateral veins on Sphenopteris‐like pinnules. Individual sporangia are of the leptosporangiate type, with a lateral annulus and a dehiscence zone of thin‐walled cells immediately adjacent to the annulus. Spores are small, trilete, triangular in outline, typically have blunt spines covering the exine, and correspond to the dispersed spore genera Acanthotriletes, Leiotriletes, or Lophotriletes. These sporangia and their spores are unlike previously described globose Botryopteris fructifications from the Middle and Upper Pennsylvanian, but are similar to sporangia produced by modern members of the Osmundaceae.

Doneggia complura gen. et sp. nov., a filicalean fern from the Upper Pennsylvanian of Ohio

The recent discovery of numerous permineralized frond segments in Upper Pennsylvanian sediments provides an opportunity to describe a new genus of the Sermayaceae and further enhance our knowledge of Paleozoic filicaleans. Specimens of Doneggia complura gen. et sp. nov. consist of up to three orders of biseriately branched frond segments with abaxial curvature of the vascular strand in proximal pinnae and large sori of superficially borne sporangia on laminar pinnules. Sori occur on pinnule lobes below vascular bundles and consist of about 25–35 sporangia. Individual sporangia are oblong, 0.6 mm long and 0.45 mm in maximum diameter, and are attached by a short stalk. As in Sermaya, the horizontal–oblique annulus consists of two rows of interfingering cells and is interrupted at one side by a narrow band of longitudinally oriented, thin-walled cells that presumably acts as a zone of dehiscence. Also, as in Sermaya, the vascular bundles have adaxially disposed protoxylem strands and crowded bordered pits on walls of the metaxylem tracheids. Spores are radial, trilete, triangular in polar view, and measure 45–63 μm in diameter. Material of this type helps demonstrate that some taxa that are currently assigned to the Coenopteridales actually represent vegetative organs of Paleozoic filicaleans.

The fine structure of ascus development in Lasiobolus monascus (Pezizales)

Ultrastructural and cytochemical studies on the ascus of Lasiobolus monascus are presented. Apothecia in various stages of development were obtained in culture and prepared for both light and electron microscopic observations. Ultrathin sections for electron microscopic inspection were often treated with silver methenamine to enhance wall characteristics. Ascus development was followed from fertilization to maturity.In this species, the ascogonium enlarges after fertilization to become the ascus mother cell. Two pores are present in the young ascus, one connecting it to the antheridium and another between the ascus and stalk cell. The ultrastructural features of these pores in the young and maturing ascus are described. During ascus enlargement, as many as four wall layers are found when poststained with silver methenamine. Only two layers are clearly distinguishable when poststained with uranyl acetate and lead citrate. The apical zone of dehiscence is characterized by a distinct annular swelling which appears during early ascosporogenesis. By spore maturation, this swelling is not evident either at the light or electron microscopic level. Instead, there appear to be both physical and chemical changes in the area of dehiscence. The wall is distinctly thinner and much more electron transparent in the area of dehiscence when treated with silver methanamine.

The apical apparatus of the suboperculate ascus

Cytochemical and ultrastructural studies have been made on the apical apparatus of six members of the suborder Sarcoscyphineae (Pezizales), an aggregate of cup fungi that displays unusually thick opercula. Various workers have placed these types into a group entitled the suboperculates, which demonstrate properties of the apical apparatus similar to both the inoper-culate and the true operculate Discomycetes. Recently, certain researchers have questioned the validity of the suboperculate apical apparatus as a stable phylogenetic indicator.Investigations were made from freshly collected material including Sarcoscypha coccinea, Phillipsia domingensis, and Wynnea americana, and from herbarium specimens including Cookeina sulcipes, Urnula craterium, and Pseudoplectania nigrella. Of the stains used for light microscope examination, Congo red proved to be the most successful for observing the opercula of fresh and revived material. Ultrathin sections for electron microscopic inspection were often treated with silver methenamine to enhance wall characteristics.The operculum is derived from the inner layer and bordered by a fibrillar zone of dehiscence which is typically absent in the outer layer. The degree of complexity of the apical apparatus ranged from a simple structure seen in Pseudoplectania to a sophisticated form found in Cookeina. The morphology of the operculum and its related components in unique enough to be implemented as a useful taxonomic criterion.

CIRCUMSCISSILE DEHISCENCE IN SOME ANGIOSPERMS

RECENTLY, the anatomy of circumscissile dehiscence in capsular fruits of some angiosperms has been described (Rethke, 1946; Subramanyam and Raju, 1952; Raju, 1952). According to Rethke in the pyxidium cannot be accounted for completely by differential drying.... A zone of mechanical weakness is formed between the lid and the base due to alignment of cells in this zone, size of the cells, number of cells concerned, thickness of walls of cells, meristematic state of the cells, or various combinations of these reasons. In some forms at least it is possible to predict the region of dehiscence of the ovary wall at a fairly early stage. In a few other forms, the zone of dehiscence is clearly differentiated during the developmental stages of the fruit. Dehiscence at a particular region is brought about by the development of sclerenchyma as in Portulaca grandiflora (Rethke, 1946) and Sphenoclea zeylanica (Subramanyam and Raju, 1952) or by meristematic cells in combination with lignified cells as in Hyoscyamus niger, Plantago species (Rethke, 1946) and Anagallis pumila (Raju, 1952). The present study deals with the histology of circumscissile dehiscence of Portulaca aleracea, P. quadrifida, P. pilosa, Anagallis a.rvensis, Celosia argentia, Allmania nodiflora (var. aspera) and Sesuvium portulacastrum. PORTULACA sp.-In different species of Portulaca the mature fruit is a pyxidium, dehiscing into an upper lid and a lower base. It is developed from a semi-inferior ovary (fig. 1). The lid and hypanthial base are multi-layered (fig. 2). PORTULACA OLERACEA.-The wall of the young ovary consists of a thick basal hypanthium and a thin upper lid (fig. 2-6). When the embrvo is mature, some thin-walled parenchymatous cells at the junction of the lid and hvpanthium become gradually lignified (fig. 3). Simultaneously, lignification also appears in the outer epidermal cells of the lid (fig. 3). Meanwhile, lignification of cells in the base extends gradually downwards (fig. 3-5). The base, which has more heavily lignified cells, is more rigid than the lid. The thin-walled cells just above the lignified group of cells form the zone of dehiscence. As a result of the pressure caused by the fully developed seeds, followed by the deepening of groove into the zone of thin-walled cells, the lid separates from the base (fig. 6). PORTULACA QUADRIFIDA.-The young ovary wall