Sieve area

Abstract: INTEREST IN both the structure and functions of phloem has heightened in the past decade, and consequently it may be timely to offer some supplementary information concerning sieve tubes in the Monocotyledoneae. Esau (1939) has recently reviewed the literature on the general subject of the structure of phloem elements in vascular plants and it is unnecessary to duplicate her work in the present paper. Some of the contributions, such as those of Hemenway (1911, 1913), MacDaniels (1918) and Crafts (1939), somewhat resemble the nature of the present work, which is in the form of a survey of the phloem in a large number of representative plants. Other articles, such as those of Schulze (1893), Ross (1883), Lange (1910), Bouvier (1915) and many more, only incidentally mention the structure of the phloem in the Monocotyledoneae. A source of general but brief information on the sieve tubes in this group of vascular plants is Solereder and Meyer (1928, 1929, 1930, 1933). Esau (1939) pointed out the confusion of terminology in the literature concerning phloem and suggested certain changes, especially with regard to sieve cells and sieve tubes. It will be profitable, therefore, to define the terms2 used in this paper before the objectives of the present work are presented. 1. A sieve area is an area in the walls of parenchyma cells, sieve cells, or sieve-tube members in which pores with connecting strands are clustered. In sieve cells and sieve-tube elements, the sieve areas are usually specialized through a more or less pronounced enlargement of connecting strands and a deposition of callose around each strand. 2. A sieve plate is a wall or portion of a wall of a sieve-tube member bearing one or more highly specialized sieve areas. There are two generally distinct types of sieve plates. One is the simple type in which the pores are uniformly distributed (fig. 6), and the other is the compound.type in which the pores are clustered in scalariform, reticulate, or any other complex manner (fig. 4 and 5). 3. A sieve cell is a cell, enucleate at maturity, in which the sieve areas of all walls are of the same degree of specialization. 4. A sieve-tube element or member is a cell, enucleate at maturity, in which certain sieve areas are

Abstract: Confocal laser scanning microscopy (CLSM) and fluorochromes were used to visualize the assimilate-conducting sieve cells of conifers in vivo. When still nucleate, the cytoplasm of these cells shows streaming and occupies the cell periphery including the pitlike, thin wall regions where sieve areas would develop. During differentiation the nuclear fluorescence and the central vacuoles disappear. At maturity and after ER-specific staining the sieve areas are the most conspicuous character of sieve cells. Those linking two sieve cells are covered on either side with prominent amounts of ER, while those leading to a Strasburger (=albuminous) cell show fluorescence on the sieve-cell side only. Within the sieve-area wall fluorescence appears also in the common median cavity which is part of the symplastic path between sieve cells. Electron microscopy (EM) depicts the ER as complexes of densely convoluted tubules of smooth ER, equally on either side of a sieve area, provided that the fixation of this sensitive tissue is appropriate. Purposeful wounding causes a swelling and vesiculation of the ER-tubules which is visible in both CLSM and EM. Electron micrographs of ER-complexes at sieve areas -in this paper demonstrated in vivo -have often been argued to be artefacts, since they should raise flow resistance considerably and are not consistent with the Munch hypothesis on phloem transport. The implications of this location for phloem transport are discussed.

Abstract: A fruit and vegetable juicer having a cover, a filter sieve, a collection bowl, a collection bowl top orifice, and a feeding tube located within the cover, wherein the cover has a helical recess extending upward from and in pulp-extraction communication with the collection bowl periphery. The helical recess in the cover also has a beginning portion and an ending portion in communication with a pulp outlet. The pulp outlet extends from the ending portion of the helical recess to provide controlled exit of the pulp from the helical recess for collection. The feeding tube is located in the cover so as to not disrupt pulp extraction through the helical recess, whereby pulp is efficiently and automatically extracted from the filter sieve area while the juice is collected in the collecting bowl.