OF MICROSCOPIC OBJECTS. 399 
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 will 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 alsinastrwm is one of these: it grows in 
water, having three leaves round the stem, then a bare por- 
tion, again another three leaves, and soon. One of these 
leaves must be plucked close to the stem, 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 be seen most beautifully when a good specimen has 
