. La plante, une illustration de la vie organique de l'animal . canaux intercellulaires riangulaires entre les cellules cylindriques tlie d'AnemonePennsylTanica. Dans certains cas, cependant, les cellules qui sont des contours hexagonaux forment des passages intercellulaires, et ceci dans un mannerso intéressant qu'il exige une description particulière. La section IFA du jeune pétiole de Sparganium ramosum placé sous le microscope, un certain nombre de triangularouvertures, connues des botanistes sous le nom de lacuna, sera vu; theseare évidemment le résultat de certaines encoches dans les parois cellulaires, qui correspondent à celles des parois de co

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. The plant, an illustration of the organic life of the animal . riangular intercellular canals between tlie cylindrical cells of AnemonePennsylTanica. In some instances, however, cells which are hexagonal inoutline form intercellular passages, and this in a mannerso interesting that it demands a particular description. Ifa section of the young petiole of Sparganium ramosum beplaced beneath the microscope, a number of triangularapertures, known to botanists as lacuna, will be seen; theseare evidently the result of certain notches in the cell walls, which correspond with those in the walls of contiguouscells. As growth progresses these notches become deeper.The lacunaa, a, a, a, (Fig. 9, ) enlarge at the expenseof the area enclosed by the cells, until at length the cells COMPARED WITH THOSE OP ANIMAIS. 41 assume a somewhat stellated aspect. In Juncus effususthe common rush, we have a beautiful example of thiskind of tissue, the cell being reduced to a six-rayed star. Fig. 9.. stellate cells from the petiole of Sparganium ramosum; a, a, cfjlacunie. as shown in Fig. 10. In this manner the large lacunaeor air-cells, common in most aquatic plants are formed. These air-cells, or lacunae, are designed not only to givebuoyancy to the leaves and stems of aquatic plants, but alsoto prevent their tissues from saturation. The air displacesthe water, which is thus excluded from entering the tissuesof the plant, otherwise than by the ordinary forces of en-dosmosis and capillarity. The formation of the lacunae isnot in this instance the result of a mere mechanical ruptureof the tissues in the interior of the plant, on the contrary, they are produced by a regular law of development, im-pressed on certain cells of the tissue, which are thusindividualized and set apart for this purpose. The stellate vegetable cell is of great importance as illustrating the formation of some of the animal tissues. It is obvious, that if the radiating prolongations of the cells, fig. 10, were

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• bookcentury1800
• bookdecade1850
• bookidcu3192
• booksubjectbiology