Oblique End Walls Research Articles

The Phloem of Etapteris leclercqii and Botryopteris tridentata

The phloem of Etapteris leclercqii and Botryopteris tridentata petioles is described from Lower Pennsylvanian coal balls. Petioles of B. tridentata are characterized in transverse section by an omega-shaped xylem trace, a phloem zone which extends from 2-10 cells in width, and 2-parted cortex. Etapteris leclercqii petioles exhibit a 4–9 cell-wide phloem zone surrounding the central clepsydroid xylem mass, and a 3-parted cortex. In both taxa a 1–2 cell layer parenchyma sheath separates the xylem from the extra-xylary tissues. The phloem of both species consists of sieve elements that average about 20 μm in diam by 200 μm in length in Botryopteris, and 100 μm in length in Etapteris, with horizontal-slightly oblique end walls. In transmitted light, the radial walls of the sieve elements form an irregular reticulate pattern enclosing elliptical lighter areas. With the scanning electron microscope, these areas appear as horizontal-slightly oblique furrows on the cell wall, with many small indentations lining the furrows. These indentations, because of their regular occurrence and size (from a few fractions of a micron up to 1.0 μm in diam), are interpreted as sieve pores, and the elliptical areas that enclose them as sieve areas. The phloem of E. leclercqii and B. tridentata is compared with that described for other fossil genera and with that of extant ferns.

Wood anatomy of theSarraceniaceae; ecological and evolutionary implications

The wood of theSarraceniaceae has a considerable number of primitive features including scalariform perforation plates, long and oblique end walls, scalariform lateral wall pitting, solitary vessels, tracheids with scalariform pitting, and diffuse axial parenchyma. Vessel elements in the genusHeliamphora have the greatest number of primitive features, while vessel elements inDarlingtonia andSarracenia appear to have modifications relating to temperate climates. The wood anatomy suggests thatHeliamphora is growing in a habitat more similar to the original habitat for the family thanDarlingtonia andSarracenia. The wood of theSarraceniaceae is similar to the wood of theTheales.

Primitive-like metaphloem sieve elements in the aerial stem ofEquisetum hyemale

Internodal metaphloem sieve elements located near the nodes of aerial stems ofEquisetum hyemale contain very oblique end walls. During maturation, the connections, or plasmodesmata, in these walls undergo little or no structural modification. By contrast, the endwall connections uniting the protoplasts of mature sieve elements elsewhere in the aerial stem ofE. hyemale are pores.

ULTRASTRUCTURE OF THE NACREOUS LEPTOIDS (SIEVE ELEMENTS) IN THE POLYTRICHACEOUS MOSS ATRICHUM UNDULATUM

The physiological phloem equivalents, leptoids, of the polytrichaceous moss Atrichum undulatum appear to be similar to the nacreous sieve elements that occur in many higher plants. These leptoids are elongated cells with nacreous thickenings on their radial and tangential walls. Their oblique end walls, which lack such thickenings, are traversed by numerous pores through which the plasmalemma, endoplasmic reticulum, and cytoplasm are continuous between adjacent leptoids of a longitudinal file. These end walls closely resemble the simple sieve areas of the sieve elements found in Polypodium vulgare. The leptoid sieve pores have a median expanded area and frequently are occluded by small amorphous protein plugs at each end. Also, callose was observed as electron‐luscent areas both on the faces of the end walls and as a thin cylinder surrounding the lateral area of each pore. Amorphous and granular cytoplasmic contents of the leptoids appear to be morphologically similar to the slime (P‐protein) found in the sieve‐tube elements of many angiosperms. Differentiating leptoids are characterized by the formation of numerous membrane‐bound protein bodies in close association with polysomes and endoplasmic reticulum. As the leptoid matures, the contents of the protein bodies become dispersed in the cytoplasm. Ultrastructurally and ontogenetically the leptoids in the gametophores of A. undulatum appear almost identical to the sieve elements of P. vulgare and therefore should be considered sieve elements rather than phloem‐like equivalents.

Observations on Metaphloem in the Vegetative Parts of Palms

Metaphloem was studied in available vegetative parts of 374 species in 164 genera of palms. Sieve elements usually have compound sieve plates except in the subfamilies Lepidocaryoideae and Nypoideae. Sieve elements in roots usually have oblique to very oblique end walls, whereas in stems and leaves they have transverse to oblique walls. Within a phloem strand the degree of compounding of a sieve plate is directly correlated with element diameter. Plastids are normally present in functioning, enucleate sieve elements. Small quantities of “slime” substances have been detected in young sieve elements in stems and petioles of a few species. Many sieve plates in functioning sieve elements lacked callose in materials quick-killed in liquid nitrogen or chilled acetic-alcohol. Definitive callose is confined to sieve elements just before their obliteration. Sieve tubes in leaf and stem are usually ensheathed by contiguous parenchyma cells while those in root have very few contiguous parenchyma cells. Two types of contiguous parenchyma cells can be distinguished by difference in cytoplasmic density, especially with the electron microscope. Cells with denser cytoplasm are interpreted as companion cells. Lignified contiguous parenchyma cells are occasionally present in metaphloem of petioles. The possible diagnostic and taxonomic features of metaphloem are discussed.

OBSERVATIONS ON METAPHLOEM IN THE VEGETATIVE PARTS OF PALMS

Metaphloem was studied in available vegetative parts of 374 species in 164 genera of palms. Sieve elements usually have compound sieve plates except in the subfamilies Lepidocaryoideae and Nypoideae. Sieve elements in roots usually have oblique to very oblique end walls, whereas in stems and leaves they have transverse to oblique walls. Within a phloem strand the degree of compounding of a sieve plate is directly correlated with element diameter. Plastids are normally present in functioning, enucleate sieve elements. Small quantities of “slime” substances have been detected in young sieve elements in stems and petioles of a few species. Many sieve plates in functioning sieve elements lacked callose in materials quick‐killed in liquid nitrogen or chilled acetic‐alcohol. Definitive callose is confined to sieve elements just before their obliteration. Sieve tubes in leaf and stem are usually ensheathed by contiguous parenchyma cells while those in root have very few contiguous parenchyma cells. Two types of contiguous parenchyma cells can be distinguished by difference in cytoplasmic density, especially with the electron microscope. Cells with denser cytoplasm are interpreted as companion cells. Lignified contiguous parenchyma cells are occasionally present in metaphloem of petioles. The possible diagnostic and taxonomic features of metaphloem are discussed.

Phloem Studies in the Pteridophytes, Part I. Equisetum

Xylary tissues of the pteridophytes have beeii studied in detail by several workers, but phloem tissue has received very little attention. The probable reason for this is the difficulties encountered in studying the anatomical structure of the phloem, for example in cutting perfect radial longitudinal and cross sections of sieve elements showing the details of sieve areas and in staining the tissues. Little is known about the phloem anatomy of Equisetum. I have studied phloem in the rhizomes and aerial shoots of E. hyemale, E. telmateia, E. arvense, and E. giganteum. This paper concerns only the latter two species. The purpose of this investigation was to gather data on Equisetum phloem that could be compared with presumably comparable tissue described in some American calamites (Agashe, 1964). Johnson (1933), in discussing the origin and development of certain tissues in E. scirpoides, mentioned the occurrence of sieve plates with small pores on the lateral walls of the sieve cells. Golub and Wetmore (1948) described the development of phloem in E. arvense. According to them, protophloem sieve cells may be 3 mm long or more. Their longitudinal walls have many, transversely elliptical, faintly staining sieve areas; such areas are also found on the oblique end walls, but they do not seem to form distinct sieve plates. Mletaphloem sieve cells are longer, larger in diameter, and have densely granular cytoplasm and very thick walls; sieve areas are more common on the end wall in metaphloem than in protophloem. There appears to be some confusion in the literature regarding the definitions of sieve cells and sieve tubes. The presently accepted definitions, according to Esau, Cheadle, and Gifford (1953), who quote Cheadle and Whitford, state that a sieve tube consists of sieve elements joined end-to-end to form a vertical tube-like structure in which sieve areas are more highly specialized on the 74

Water-conducting System of Symphyogyna

THE gametophytes of the liverwort genera Hymenophyton, Podomitrium, Pallavicinia and Symphyogyna contain an internal water-conducting system, which is strikingly analogous to the xyleni of simple vascular plants. This system is composed of one or more strands of narrow diameter, elongate, thick walled, densely pitted conducting cells that are devoid of protoplasmic contents at maturity. The presence of this system was first noted by William Jackson Hooker1 in Jungermannia (now Pallavicinia) lyellii. Leitgeb2 pointed out that the cells of the strand were elongate, possessed oblique end walls and that the cell walls were considerably thickened and possessed close-set pores. Tansley and Chick3 reported that the contents of the cells of the conducting strand disintegrate during development and demonstrated that the strand is actually an efficient water-conducting unit within the thalli.

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.

Comparative Anatomy and Phylogeny of the Casuarinaceae

1. The chief purposes of this investigation have been to contribute toward a better understanding of the evolutionary status of the Casuarinaceae; to present a thorough anatomical description of the family; and to tabulate, at least provisionally, the outstanding characteristics of twenty-nine species. 2. The anatomy of the secondary xylem of the old wood (wood at some distance from the pith) may be summarized as follows: Growth rings are poorly defined or absent; both tracheids and fibertracheids are found in all but one species, in which only tracheids occur; tracheids generally predominate, and the larger, thinner-walled tracheids are vasicentric; the fiber-tracheids often have very thick walls; the fibrous elements are extremely short to moderately long, mostly short to medium-sized; spiral thickenings occur in the fibrous elements of six species. The range of species means for the number of vessels per square millimeter is from moderately few to very numerous; vessel distribution is universally solit...

On the multiperforate plates occurring in the xylem vessels of some monocotyledonous roots

The occurrence and structure of multiperforate plates in the xylem vessels of the roots of some monocotyledons are described. Such plates are present in all the vessel segments of the roots of many members of the family Araceae and inCrinum asiaticum. In all these plants vessel segments with simple perforations have not been observed. The vessel segments as found in these roots may be of three types : (i) those having oblique end walls at both ends; (ii) those having oblique end wall at one end and transverse or slightly inclined end wall at the other; (iii) those having transverse or slightly inclined end wall at both ends. The perforation plates of these segments may be scalariform, scalariform with branched bars, or reticulate. The bars of the plates can be correlated to the scalariform-reticulate thickening of the lateral walls of the vessel segments. These types of vessel segments are regarded as forming a primitive feature. Further it is concluded that the xylem vessels of roots have developed phylogenetically from typical scalariform tracheids by the loss of pit membranes at their ends.