The parenchymo-vascular cambium and its derivative tissues in stems and roots of Bougainvillaea glabra Choisy (Nyctaginaceae)

In the shoots and roots of <i>Bougainmllaea</i>, the parenchymo-vascular cambium produces thinwalled secondary parenchyma to one side and the secondary vascular bundles embedded in the "conjunctive tissue" to the other. Periclinal division of a single cambial cell in one radial row brings about periclinal divisions of the adjacent cells of the neighbouring rows. Anticlinal division of a single cambial cell at one level, on the other hand, causes anticlinal. divisions of the adjacent cells of the overlying and underlying tiers.

Organization of the root apical meristem in Linum usitatissimum L. grown at 25°C and 7°C

In the first days of intensive growth of the Linum usitatissimum root, the central part of the apical meristem exhibits usually a 4-tier organization. When growth ceases reorganization of the cell arrangement occurs. It starts by periclinal division of the subprotodermal initials, whose derivatives are forming the secondary columella in the central part of the root cap.

Pericarp ontogeny and histochemistry of the exotesta and pseudocaruncle of Euphorbia milii (Euphorbiaceae)

Several types of fruit occur in Euphorbiaceae, notably the explosively dehiscent dry fruit, and different seed-coat anatomies with taxonomic importance. This paper aims to describe the pericarp ontogeny and structure in Euphorbia milii Desmoul., and evaluate the presence of the secretory exotesta and caruncle. The fruit is a schizocarp, whose the pericarp development begins with a periclinal division of the inner epidermal cells. The derived cells divide, forming about four layers of obliquely elongated cells. Then, the adjacent parenchyma cells elongate, giving rise to a palisade layer and finally, the cells between this layer and the vascular strands undergo mitosis, originating about four layers of elongated cells perpendicularly to the inner oblique cells. These three zones lignify, while the region between the vascular strands and the exocarp, where idioblasts, hypodermis and laticifers are present do not show significant changes. Before the dehiscence, a lysis of cells of the septa and the desiccation of the fruit occur, which causes contraction of the non-lignified tissues and tension between the lignified zones, promoting rupture of each mericarp from central columella and on the dorsal strand, ejecting the seeds. The seeds have pseudocaruncle and the exotesta secretes mucilage, facilitating their imbibition.

Ontogenesis of the fruit pulp layer of Hymenaea stigonocarpa (Fabaceae: Caesalpinioideae)

Hymenaea, a genus of major economic importance, has been the subject of several botanical studies. However, there is disagreement over the origin of the edible fruit pulp of Hymenaea, as there are no ontogenetic studies on this organ. According to some authors, the edible layer results from transformations of the mesocarp and endocarp, while according to others, it is considered a seed aril. There are still others who regard this layer as originating from an undefined region of the pericarp. To understand the nature and origin of the pulp layer, Hymenaea stigonocarpa Mart. ex Hayne ovaries and fruit were processed according to standard techniques. The production of the fruit pulp layer starts immediately after anthesis. During anthesis, the inner epidermal cells of the ovary show periclinal division and form a new layer of cells towards the mesocarp; this remains meristematic and initiates cell production by predominantly periclinal divisions, producing a compact tissue towards the locule. This tissue will become the fruit pulp layer, the inner endocarp. The seed coat shows typical testal structure without evidence of aril formation. This allows us to conclude that the fruit pulp layers are exclusively made from part of the endocarp. We also observed resin cavities on outer mesocarp and outer endocarp.

Microsporogenesis in genic male-sterile lines of barley (Hordeum vulgare)

Pollen development has been studied by various microscopical techniques in five genic male-sterile lines and in male-fertile lines of barley (Hordeum vulgare L.). Two of the male-sterile lines (msg,,ho and msg,,fz) exhibited apparently identical abnormalities: defective cytokinesis at the end of meiosis 1. Another male-sterile gene (msg,,fg) also appeared to cause defects at this stage; in this case nuclear restitution was incomplete. In the male-sterile line msg,,gf a failure of the periclinal division of the inner secondary parietal layer occurred, so that a tapetal layer was not formed. Development was normal through meiosis in anthers from msg,,fp plants until the early vacuolated microspore stage when normal sporopollenin production was inhibited.

An Experimental Assessment of the Status of the Species Enteromorpha Intestinalis (L.) Link and Enteromorpha Compressa (L.) Grev.

Many workers have experienced difficulties in trying to identify species within the genus Enteromorpha. The difficulties arise from our lack of knowledge of the range of variation for the characters used to delimit the taxa and of the sources of the variation shown.Enteromorpha intestinalis (L.) Link was originally described by Linnaeus (1753) under the name Ulva intestinalis as ‘Ulva tubulosa simplex’ and Enteromorpha compressa (L.) Grev., also by Linnaeus (1753) under the name Ulva compressa as ‘Ulva tubulosa ramosa compressa’. In their interpretations by later authors, the two species differ only in that the former is unbranched and the latter branched. In their cell size, in the unordered arrangement of the cells and in the single pyrenoid in the chloroplast, they seem to belong together. Whether or not a plant is branched would seem to be a straightforward character to use in practice, but for an alga of this kind this is not necessarily so. In its development the unbranched tube of the thallus begins life as a zoospore or zygote which at first divides transversely to form a short uniseriate filament and later by radial longitudinal divisions, the subsequent expansion of which leads to the formation of the hollow tube. In the formation of branches, individual cells, usually towards the base of the frond, divide by a single periclinal division. The outer cell of the pair thus formed then divides transversely forming a single-celled filament, later dividing by radial longitudinal divisions and repeating the structure of the main axis.

Initiation of floral organs in Nicotiana tabacum

Floral buds of Nicotiana tabacum were fixed, sectioned, and stained by routine procedures, then analyzed microscopically. Initiation and emergence of all four classes of floral organs involved periclinal division in the second tunica layer (T2) and division of corpus cells. The extent of periclinal T2 divisions was different in different organs. Plasmolysis of tunica and corpus cells was observed at organ sites. The results generally parallel those of other studies.

Floral histogenesis in the Monocotyledons. IV. The Liliaceae

An account is presented of floral histogenesis in Bulbine bulbosa R.Br. and Stypandra glauca R.Br. The apex of the floral axis in both species has a two-layered tunica, and bracts arise through the periclinal division of cells of the inner layer of the tunica (hypodermis). In Bulbine, axillary flower primordia are initiated in the periclinal division of subhypodermal cells; in Stypandra the flower primordia are terminal and arise directly from the apices of branches of the inflorescence. In both species the perianth'members originate, in the same manner as the bracts, through periclinal divisions in cells of the hypodermis. Periclinal divisions may occur in the cells of the outer tunica layer (dermatogen) after the prinlordia are well formed. Divisions in subhypodermal cells in the area of perianth initiation are associated with the formation of a provascular strand and it is doubtful if such divisions contribute anything to the tissue of the perianth primordium itself. The stamens are initiated in the periclinal division of both hypodermal and subhypodermal cells. In Bulbine the carpels develop through periclinal divisions in the hypodermis and dermatogen. The placentas appear to arise through divisions in subhypodermal cells as structures adnate to the carpels. In Stypandra the carpels arise in a quite different manner through the periclinal division of subhypodermal cells. The margins of the carpels develop as the placentas and there is no suggestion in the early ontogeny of the gynaecium that the placentas have an independent origin.

Floral histogenesis in the Monocotyledons. II. The Cyperaceae

An account is presented of floral histogenesis in Scirpus validus Vahl, Cyperus eragrostis Lam., and Carex appressa R. Br. The cells of the apex of the spikelet in the three species are arranged in a two-layered tunica over a central corpus. Histogenetically the outer and inner tunica layers behave differently and are termed dermatogen and hypodermis respectively. The same three tissue zones are recognized in the flower primordia. Periclinal division of dermatogen and hypodermal cells gives rise to (i) the glumes or floral bracts and carpels in all species, (ii) the perianth members in Scirpus, and (iii) the perigynium in Carex. These are all classified as foliar organs. Periclinal divisions in cells of the outer corpus layers, and inclined and periclinal divisions in the hypodermis, characterize the formation of flower and stamen primordia. Periclinal division of dermatogen cells never occurs. These organs are regarded as cauline. The ovule develops directly from the growing point of the flower primordium and its integuments arise in the foliar fashion. The general pattern of histogenesis is compared with that in the Gramineae. Variations within this pattern and the interpretation of the floral structures are discussed.