The Encyclopaedia Britannica; .. A dictionary of arts, sciences and general literature . CLEMENTS.] BOTANY or as small wbeu the cell-wall is very thick. Suchcells are termud porous or pitted or dolled ceWs {&g. 21). Inold cells, after the protoplasm has disappeared, the portionof the cell-wall which remained thin is often absorbed,and thus there is a true perforation of the perforations often occur in groups both upon thecell-wall and upon the septum between superposed cells, andgive rise to a remarkable sieve-liko structure, in whichcase they are termed sieve-cells- Th
The Encyclopaedia Britannica; .. A dictionary of arts, sciences and general literature . CLEMENTS.] BOTANY or as small wbeu the cell-wall is very thick. Suchcells are termud porous or pitted or dolled ceWs {&g. 21). Inold cells, after the protoplasm has disappeared, the portionof the cell-wall which remained thin is often absorbed,and thus there is a true perforation of the perforations often occur in groups both upon thecell-wall and upon the septum between superposed cells, andgive rise to a remarkable sieve-liko structure, in whichcase they are termed sieve-cells- The latticed cells of someauthors are of a similar nature. When superposed poroust>r sieve-cells coalesce by complete obliteration of the septum,then a pitted vessel, sievo tube, or duct u formed (fig. 22).These ducts are usually of a larger size than other ves-. Fig. 23. Fig. 22. na. 21.—Porous or pitted cell from the Mistlelo. Flo. 22.—HonilifoMn dotted or pitted vessel from the Melon. >io. 23.—Section of a Bamboo, showing an angular network of cells, and the round apeiturca of pitted vessels. sels; they are well seen in the inner phloem layers and inthe wood of trees, and they constitute the large roundedopenings which are seen in the section of thestems of the Oak, Poplar, Willow, &c. They also abound inthe Bamboo (fig. 23), and in other plants of rapid names of bothrenchyma and taphrencht/ma have beengiven to a tissue composed of such cells. Not unfrequentlycontractions are visible on the outside of the vessel (fig. 22),indicating its formation by coalescence of superposed cells.,To vessels exhibiting contractions of this kind, whetherspiral or pitted, the terms moniliform. and vermiform havebeen applied ; and the tissue composed of these has been denominated phleboidal. In the ducts
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectencyclo, bookyear1902
