SIEVE-ELEMENT ONTOGENY IN THE ROOT OF EQUISETUM HYEMALE

Roots of Equisetum hyemale L. var. affine (Engelm.) A. A. Eat. were fixed in glutaraldehyde, postfixed in osmium tetroxide, and sieve elements of various ages were examined with the electron microscope. Young sieve elements are distinguished by their position within the vascular cylinder and by the presence of numerous refractive spherules, which originate within dilated portions of the endoplasmic reticulum (ER). Early in development, the sieve-element walls undergo a substantial increase in thickness. This is followed by the appearance of massive ER aggregates in the cytoplasm and then by a phase involving stacking and sequestering of the remaining ER. Nuclear degeneration is initiated shortly after the appearance of the ER aggregates. The chromatin condenses into masses of variable size along the inner surface of the nuclear envelope. The envelope then ruptures and chromatin is released into the cytoplasm. During the period of nuclear degeneration, mitochondria and plastids undergo structural modification, while components such as dictyosomes, microtubules, and ribosomes degenerate and disappear. The remaining cytoplasmic components assume a parietal position in the cell, leaving the lumen of the cell clear in appearance. At maturity, the plasmalemma-lined sieve element contains plastids, mitochondria, some ER, and refractive spherules. At this time many of the refractive spherules are discharged into the region of the wall. Pores between sieve elements occur largely on the end walls. During pore development, tubules of ER apparently traverse the pores, but because of the presence of massive callose deposits in the material examined, the true condition of mature pores could not be determined. The connections between mature sieve elements and pericycle cells are characterized by the presence of massive wall thickenings on the pericycle-cell side. Plasmodesmata in the wall thickening are matched by pores on the sieve-element side. Ontogenetic and cytoplasmic factors argue against use of the term “companion cell” for the vascular parenchyma cells associated with the sieve elements.     

SHOOT TIP ABORTION IN ULMUS AMERICANA

Millington , W. F. (Marquette U., Milwaukee, Wis.) Shoot tip abortion in Ulmus americana. Amor. Jour. Bot. 50(4): 371–378. Illus. 1963.—Phenological observations of American elm have shown that the phenomenon of shoot tip abortion in which the distal several plastochrons of each shoot turn yellow and abort, inducing sympodial growth, occurs over a period of several weeks starting at the time fruits are shed from older trees. Time of abortion varies among plants of different age, among individuals of the same age, and among shoots on the same individual. In the latter case, time of abortion is inversely correlated with the vigor of the shoot, the most vigorous shoots on a branch being the last to abort. Abortion is first evident in the yellowing of the entire shoot tip. Cytohistological studies show that necrosis commences at the sixth to eighth node back of the apex, where it is apparent in autolysis of internal cells of the stipules. Necrosis progresses acropetally in the stipules and young leaves and ultimately involves the leaf primordia at the shoot apex. Mitosis ceases in the shoot apex and its meristematic appearance is lost. These changes follow in basipetal sequence in the axillary buds down to the bud below the abscission site. This bud remains active and will resume growth the following season. The abscission site is evident externally as a green-yellow boundary in the basal part of the internode. No protective layer is present at the time of abscission, but it develops after the shoot tip abscises. There is no indication of blocking of vascular tissues before shoot tip abortion and limitation of water supply probably is not a causal factor. Photoperiod studies show that shoot tip abortion is accelerated in short days and delayed but not prevented in long days. Greenhouse experiments show that abortion is delayed also in seedlings, in plants supplied with organic fertilizer, or grown with the roots unconfined. Plants grown in a nutrient solution deficient in nitrogen aborted ahead of controls and plants deficient in calcium. Although shoot tip abortion occurs coincident with fruit drop, there is no indication of a causal relationship. The literature relating to shoot tip abortion is discussed in relation to the above observations.     

云南树鼩肝脏结构的光,电镜观察

本文报告了树肺脏的一般结构和超微结构。与人和灵长目相似，其肺实质也是由导气部和呼吸部构成。但不同的是其细支气管粘膜形成很高的皱襞。在电镜下Ｃｌａｒａ细胞电子密度高，顶部胞质中含有大量膜包颗粒，这些结构与大白鼠和家兔的结构相似。许多毛细血管外方都包绕着基膜和肺泡Ⅰ型上皮细胞的胞质。气血屏障由肺泡上皮细胞、融合的基膜和内皮细胞胞质构成。说明树肺脏不但是呼吸器官，也是一些激素和介质产生及代谢的重要器官。本文为研究树的正常生理功能及分类提供形态学资料。     

A STUDY OF THE STRUCTURE OF SPLENIC SINUSES IN MAN AND IN THE ALBINO RAT WITH THE LIGHT MICROSCOPE AND THE ELECTRON MICROSCOPE

The splenic sinuses in the spleens of 5 human beings and 7 albino rats have been studied in the light microscope and electron microscope after fixation in Dalton's fluid and Palade's fluid and embedding in n-butyl methacrylate. Splenic sinuses are tortuous vascular channels of large but variable diameter which represent the first venous vessels in the spleen and make up almost the entire red pulp in man and in rats. These vessels are composed of reticulo-endothelial cells flattened to endothelial form and sheathed by a netted reticulum. The luminal surface of the endothelium is made highly irregular by delicate and variable cytoplasmic protrusions, slender corridors separating adjacent endothelial cells, anastomotic openings to other sinuses, bulgings of entire cells, and even thrusts of endothelium spanning the sinai lumen. The supporting reticulum presents a well developed latticed appearance in tangential sections of sinuses, but in most cuts is punctate or linear. The reticulum is composed of strands without limiting membranes, which, in substance, are amorphous and resemble basement membrane. Material identical in appearance to the substance of the reticulum may be present in the endothelium, suggesting that the reticulum is formed by endothelial cells. The endothelium also contains deposits of presumed ferritin and hemosiderin. The extreme luminal bulgings of endothelium suggest production of circulating monocytes or lymphocytes by detachment of endothelial cells. Sinuses are patent and collapsed to varying degrees. Patent sinuses are separated by collapsed sinuses and these collapsed sinuses appear to constitute splenic (Billroth) cords.     

STRUCTURE AND DEVELOPMENT OF THE SIEVE-ELEMENT PROTOPLAST IN THE HYPOCOTYL OF PINUS RESINOSA

Hypocotyl tissue of Pinus resinosa Ait. was fixed in glutaraldehyde-paraformaldehyde and postfixed in osmium tetroxide for electron microscopy. Although young sieve cells contain all the components characteristic of young, nucleate cells, they can be identified early in their development. Increase in wall thickness occurs early and rapidly. Concurrently, the plastids, which already contain starch granules, form both crystalline and fibrillar inclusions. As the sieve cell approaches maturity, an extensive network of smooth, tubular endoplasmic reticulum (ER), which becomes mostly parietal in distribution, is formed. At maturity, massive aggregates of this ER occur on both sides of sieve areas. These ER aggregates are interconnected with one another longitudinally by the parietal ER. In addition, the mature, plasmalemma-lined sieve cell contains a degenerate nucleus, mitochondria, and intact plastids. Dictyosomes, ribosomes, and vacuolar membranes are lacking. P-protein is not present at any stage of development.     

ONTOGENY AND STRUCTURE OF THE SECONDARY PHLOEM IN EPHEDRA

The secondary phloem in Ephedra is atypical of the gymnosperms in general and exhibits several angiosperm-like characteristics. The ray system of the conducting phloem consists of parenchymatous, multiseriate rays. The axial system contains parenchyma cells, sieve cells, and unusual albuminous cells reminiscent of the specialized parenchyma cells found in some angiosperms. These cell types may intergrade with each other. P-protein in the developing sieve element appears early in the form of a single, ovoid slime body. Later, smaller slime bodies appear and quickly disperse. In the mature sieve element the single, ovoid slime body is lost, and P-protein is then evident in the form of a parietal cylinder, thread-like strands, amorphose globules, or a slime plug. Necrotic-appearing nuclei are commonly found in mature sieve cells.     

ONTOGENY AND STRUCTURE OF THE SECONDARY PHLOEM IN PYRUS MALUS

Evert , Ray F. (U. Wisconsin, Madison.) Ontogeny and structure of the secondary phloem in Pyrus malus. Amer. Jour. Bot. 50(1): 8–37. Illus. 1963.—The secondary phloem of apple consists of sieve-tube elements, companion cells, phloem parenchyma cells, fiber-sclereids, and ray parenchyma cells. The sieve-tube elements are generally long, slender cells with very oblique end walls and much-compounded sieve plates. All sieve-tube elements initially possess nacreous thickenings. Similar wall thickenings were observed in the differentiating fiber-sclereids and xylem elements. Of the 245 sieve-tube elements critically examined, 242 were associated with companion cells. All of the companion cells were shorter than their associated sieve-tube elements. Young companion cells possess slime bodies which later become dispersed. Callose is often found on the sieve-tube element side of the common wall between sieve-tube element and companion cell. In several collections, callose was found on both sides of that wall. The parenchyma cells are of 3 types: crystal-containing cells; tannin-and/or starch-containing cells; and those with little or no tannins or starch. Any type parenchyma cell may be on to genetically related to a sieve-tube element, that is, may be derived from the same phloem initial as the sieve-tube element. Morphologically, the phloem parenchyma cells intergrade with the companion cells, the tannin- and starch-free parenchyma cells often being difficult to distinguish from companion cells. Most of the tannin- and starch-free parenchyma cells collapse when the contiguous sieve-tube elements become nonfunctional. The fiber-sclereids arise from parenchyma cells which overwinter on the margin of the cambial zone and differentiate in nonfunctional phloem.     

FLUID FLOW IN THE OUTERMOST XYLEM INCREMENT OF A RING-POROUS TREE,ULMUS AMERICANA

Hydraulic conductivity through the outermost growth ring of Ulmus americana was quantified to determine the significance of this single growth increment to fluid flow in xylem of a ring-porous tree. Gravity flow rates through trunks deprived of the outermost growth ring dropped to 8% of the rate achieved in control trunks whose cross section was intact. However, colored dye, fed through stem segments, appeared in up to 4-yr old wood, corroborating earlier reports that fluid flows through more than just the outermost growth ring of ring-porous trees. Finally, the pathway of flow through older rings was shown to consist of narrow latewood elements while the wider and more hydraulically significant earlywood vessels came into play only in the outermost growth ring of U. americana. These data indicate that the outermost growth ring of Ulmus is responsible for over 90% of xylem transport in this ring-porous tree, because wide earlywood vessels function only for one growth season.     

STRUCTURE AND ONTOGENY OF LATICIFERS IN CICHORIUM INTYBUS (COMPOSITAE)

The branched anastomosed laticifer system in the primary body of Cichorium intybus L. originates in embryos from files of laticiferous members at the boundary between phloic procambium and ground meristem. Upon seed germination, laticiferous members develop perforations in the end walls which become entirely resorbed. Perforations also develop in the longitudinal walls of contiguous laticiferous members and from lateral connections between developing laticifer branches. Additional laticiferous members originate as procambium differentiation proceeds, and their differentiation follows a continuous acropetal sequence in leaf primordia of the plumule. In roots, laticifers closely associated with sieve tubes in the secondary phloem originate from derivatives of fusiform initials in the vascular cambium. These laticifers develop wall perforations and in a mature condition resemble laticifers in the primary body. As the girth of the root increases, laticifers toward the periphery, unlike associated sieve tubes, resist crushing and obliteration. Laticifers vary in width from about 4 to 22 μm; the widest ones occur in involucral bracts and the narrowest ones in florets. There was no evidence that intrusive growth occurs during development of the laticifer system, although such growth may occur during development of occasional branches which extend through ground tissue independent of phloem and terminate in contact with the epidermis. Presence of amorphous callose deposits is related to aging of laticifers and mechanical injury.     

ONTOGENY AND STRUCTURE OF CONIFEROUS SIEVE CELLS

Studies of the secondary phloem of 6 species of conifers revealed that mature sieve-cell protoplasts contain internal strands which are derived ontogenetically from slime bodies of immature cells. These strands, each measuring about 0.3 μ in diameter, traverse the cell and run from cell to cell through sieve-area pores. Coniferous sieve cells have much in common—both ontogenetically and structurally—with dicotyledonous sieve-tube members.     

LIGHT AND ELECTRON MICROSCOPE STUDIES OF THE CELL WALL STRUCTURE OF THE ROOT HAIRS OF RAPHANUS SATIVUS

Dawes , Clinton J., and Edwin Bowler . (U. of California, Los Angeles.) Light and electron microscope studies of the cell wall structure of the root hairs of Raphanus sativus. Amer. Jour. Bot. 46(8): 561–565. Illus. 1959.—The structure and development of the cell wall of the root hair of Raphanus sativus were studied under the light and electron microscopes. The outer layer of the root hair consists of mucilage which covers the entire hair and forms a thick cap at the tip. Beneath the mucilage a thin cuticle covers the inner layers of the cell wall. These layers consist of cellulose microfibrils, varying in pattern, in a granular matrix, presumably pectic in nature. The microfibrils of the outer layer, apparently laid down at the tip, are reticulate in arrangement. In mature regions of the root hair, the wall is thickened by an inner layer of parallel and longitudinally orientated microfibrils. Pores in the cellulose wall are evident and increase in number and size near the base of the hair.     

A LIGHT AND ELECTRON MICROSCOPE STUDY OF INTERLAMELLAR POLYGLUCOSIDE BODIES IN OSCILLATORIA CHALYBIA

A light and electron microscopic study of interlamellar granules in Oscillatoria chalybia was made to determine their physiological nature. Oscillatoria chalybia was cultured under continuous light in media of high nitrogen content, moderate nitrogen content and low nitrogen content. Cultures growing vigorously in a medium of moderate nitrogen content were placed in darkness for an additional 96 hr. Periodic acid-Schiffs reagent tests were made on specimens from these 4 cultural conditions. Electron microscopic studies of interlamellar granules were correlated with the cytochemical tests. It is shown that diastase digestion will eliminate the PAS-positive substance and the interlamellar granules. Conclusions are that the interlamellar granules are polyglucoside in nature and that they vary in number and size with available nitrogen, light intensity and age of culture in such a way as to indicate that they are food reserves.     

叶表皮结构在榆属分类中的应用

本文利用扫描电子显微镜对榆属9种1变种的成熟叶表皮结构进行了观察,认为榆属叶表皮结构在扫描电镜下存在着明显的差别,可以作为榆属分种的辅助特征。     

LIGHT AND ELECTRON MICROSCOPE STUDIES OF MORPHOLOGICAL CHANGES OF MITOCHONDRIA DURING SPERMATOGENESIS IN THE GRASSHOPPER

1. Observations on the morphological changes of mitochondria preparatory to the formation of the nebenkern, as well as changes within the nebenkern, are reported. 2. Mitochondria enlarge and divide during the meiotic divisions. 3. The mitochondria of the spermatid elongate, become filamentous, form a crescent, and partially encircle the nucleus. 4. Nodes which develop on either end of the crescent become entwined as they move toward each other. 5. The two nodes coalesce to form a filamentous or early type nebenkern which is described by others as chromophilic. 6. Internal rearrangement and partial dissolution of the filaments result in the development of the late or chromophobic nebenkern which separates into two distinct bodies. 7. The nebenkern moieties send out processes toward the centrosome, and after making contact, elongate and occupy part of the space between the tail filaments and sheath of the spermatozoon.