1G8 PLANT-LIFE. [lESSON 27. 



under (lie glass like strings of blue beads, each bead being a cell. 

 But here a microscope magnitying six or eight hundred times in 

 diameter is needed to see the current distinctly, 



484. The movement belongs to the protoplasm (476), or jelly-like 

 matter under the cell-wall. As this substance has just the same 

 composition as the flesh of animals, it is not so strange that it should 

 exhibit such animal-like characters. In the simplest water-plants, 

 of the Sea-weed family, the body which answers to the seed is at 

 first only a rounded little mass of protoplasm. When these bodies 

 escape from the mother plant, they often swim about freely in the 

 water in various directions, by a truly spontaneous motion, when they 

 closely resemble animalcules, and are often mistaken for them. After 

 enjoying this active life for seveial hours, they come to rest, form 

 a covering of cellulose, and therefore become true vegetable cells, 

 fix themselves to some sup[)ort, germinate, and grow into the 

 perfect plant. 



485. Absorption, Conveyance of llic Sap, &c. Although contained in 



cells with closed walls, nevertheless the fluids taken in by the roots 

 are carried up through the stein to the leaves even of the topmost 

 bough of the tallest tree. And tlie sap, after its assimilation by the 

 leaves, is carried down in the bark or the cambium-layer, and dis- 

 tributed throughout the plant, or else is conveyed to the points where 

 growth is taking place, or is accumulated in roots, stems, or wherever 

 a deposit is being stored up for future use (71, 104, 128, 4G9). 



486. That the rise of the sap is pretty rapid in a leafy and growing 

 plant, on a dry summer's day, is evident from the amount of water it 

 is continually losing by exhalation from the foliage (447) ; — a loss 

 which must all the while be supplied from the roots, or else the 

 leaves would dry up and die ; as they do so promptly when sepa- 

 rated from the stem, or when the stem is cut off from the roots. 

 Of course they do not then lose moisture any faster than they 

 did before the separation ; only the supply is no longer ke|)t 

 up from below. 



487. The rise of the sap into the leaves apparently is to a great 

 degree the result of a mode of diffusion which has been called En- 

 dosmose. It acts in this way. Whenever two fluids of different 

 density are separated by a membrane, whether of dead or of living 

 substance, or are separate(^ by any porous partition, a flow takes 

 {)lace through the partition, mainly towards the heavier fluid, until 

 that is brought to the same density as the other. A familiar illus- 



