OF MICROSCOPIC OBJECTS. 199 



as it is usually termed, the circulation of the sap, of plants. 

 This is shown in certain vegetable growths as a constant 

 stream of thick fluid, wherein small globules are seen; 

 which stream flows round the individual cells, or up the 

 leaf, turning at the extremity, and down again by a different 

 but parallel channel. There is little or no difficulty in 

 showing this in many plants; but some are, of course, 

 better than others, and require a different treatment; we 

 will, therefore, notice a few of these. Perhaps the best of 

 all is the Vallisneria spiralis, which is an aquatic plant, 

 frequently grown in, but not really belonging to, this 

 country. As it somewhat resembles grass, the leaf is not 

 used in its natural state, but a thin section cut lengthwise 

 with a razor or other sharp instrument; this section, how- 

 ever, is much better when the outer surface has been first 

 removed. It should then be laid upon a slide with a drop 

 or two of water, and covered with a piece of thin glass. 

 Often the cutting of the section seems to be such a shock to 

 the leaf that no motion is visible for awhile, but in a short 

 time the warmth of an ordinary sitting-room ^rill revive it, 

 and with a quarter-inch object-glass the currents will be 

 rendered beautifully distinct. Where the stream is un- 

 usually obstinate, the warmth may be slightly increased, but 

 too high a heat destroys the movement altogether. In the 

 summer, any of the leaves show this circulation very 

 well ; but in the winter, the slightly yellow ones are said to 

 be the best. 



The Vallisneria requires to be cut in sections to show 

 this circulation ; but there are many plants of which it is 

 but necessary to take a fragment and lay it upon the slide. 

 The Anacharis alsinastrum is one of these : it grows in 

 water, having three leaves round the stem, then a bare por- 

 tion, again another three leaves, and so on. One of these 

 leaves must be plucked close to the stein, and laid upon a 

 slide with a drop of water. Thin glass should be placed 

 upon it, and along the mid-rib of the leaves the circulation 

 may bo seen most beautifully when a good specimen has 



