. An introduction to vegetable physiology. Plant physiology. THE GBNEEAL STRUCTURE OP PLANTS 13 It is only by its powers of responding to such impressions that the whole organism is able to place itself in harmony with its environment. Finally, it carries out the processes of reproduction. The primary needs of a plant are fairly simple. If we study the life and the behaviour of one of the free-swim- ming organisms of which we have already spoken, we see that its first requirement is water. In this it lives ; from this it draws its supplies of nutriment and into this it pours forth its excreta.
. An introduction to vegetable physiology. Plant physiology. THE GBNEEAL STRUCTURE OP PLANTS 13 It is only by its powers of responding to such impressions that the whole organism is able to place itself in harmony with its environment. Finally, it carries out the processes of reproduction. The primary needs of a plant are fairly simple. If we study the life and the behaviour of one of the free-swim- ming organisms of which we have already spoken, we see that its first requirement is water. In this it lives ; from this it draws its supplies of nutriment and into this it pours forth its excreta. The arrangement of the protoplasm in the cell in one of the higher plants points to a similar need. If we regard the arrangement whether in the young or the adult cell, we notice particularly the very close relation of the protoplasm to water. The young cell enclosed in its cell- membrane speedily shows a tendency to accumulate water in its interior, and gradually drops appear in its sub- stance which lead ultimately to the formation of a vacuole always full of liquid (figs. 15, 16). This store of water in the interior of a cell is of almost universal occurrence in the lowly as well as the highly organised plant. The constitution of proto- plasm, so far as we know it, depends upon this relation, for the appa- rently structureless substance is always saturated with water. It is only while in such a condition that a cell can live ; with very rare exceptir .s, if a cell is once completely dried, even at a low temperature, its life is gone, and restoration of water fails to enable it to recover. The constancy of the occurrence of the vacuole in the cells of the vegetable organism is itself an evidence that such cells are completely dependent upon water for the maintenance of life. The cell-wall, though usually. Fig. 16.—Adult VsaETABLE Cells. x 500. (After Sachs.) hy cell-wall; p, protopJasm; k k', nucleus, with nucleoli; s' 3, Please note that these images are extrac
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