. An introduction to vegetable physiology. Plant physiology. THE GENEEAL STEUCTURE OF PLANTS. Fig. 10.—Colonies of Protococcus. X 750. of these units of construction, a variety which finds its expression in the multiplicity of existing forms, and the differences of dimensions which various organisms exhibit. The simplest plants, as we have seen, are unicellular, and many remain in this condition throughout the whole of their existence. When they have attained a certain size the cell or protoplast divides into two. Sometimes these two become separated from each other, and we have two plants whe
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. An introduction to vegetable physiology. Plant physiology. THE GENEEAL STEUCTURE OF PLANTS. Fig. 10.—Colonies of Protococcus. X 750. of these units of construction, a variety which finds its expression in the multiplicity of existing forms, and the differences of dimensions which various organisms exhibit. The simplest plants, as we have seen, are unicellular, and many remain in this condition throughout the whole of their existence. When they have attained a certain size the cell or protoplast divides into two. Sometimes these two become separated from each other, and we have two plants where but one existed before. Plants with this habit remain unicellular, and the division of the cell is equiva- lent to the reproduction of the plant. The unicellular condi- tion in other cases is transitory, and the plant soon comes to consist of two, four, or more cells, in consequence of the products of each division re- maining attached together. We get in this way a small colony of cells, each hke the others both in structure and in function. When the power of division is limited the resulting colony consists of a limited number of cells, and is often found surrounded by a common cell-wall or membrane. This condition is seen in such plants as Chroococcus, Protococcus, and other humble Algas (fig. 10). A colony of somewhat higher type, though still of microscopic size, is found in the form of a hollow sphere (fig. 11), the wall of which is one cell thick (fig. 11, a). This organism, known as Volvox, shows a little higher differentia- tion than those last described, the cells being furnished with cilia by means of which the little sphere can propel itself through the water. In other cases the association of a number of protoplasts is not complicated by the formation of any cell-wall. Fig. 4, A shows an aggregation of a number of naked proto- plasts which have combined to form a plasmodium. These organisms are found creeping about upon moist surfaces;. Please note that these
