200 PREPARATION AND MOUNTING 
been chosen; but it requires rather more power than the 
Vallisneria. This plant is very common in many parts of 
the country, a great number of our ponds and streams being 
literally choked up by it. In the Chara vulgaris and two or 
three of the Nitelle, &c., this phenomenon may also be seen 
with no preparation except plucking a part from the stem 
and laying it wpon a slide, as with the Anacharis, In using 
the Frog-bit, the outer part of the young leaf-buds must be 
taken to obtain the best specimens for this purpose; but a 
section of the stem will also show the circulation, though not 
so well. The plants before mentioned are all aquatic, but 
the same movement of the globules has been observed in 
several kinds of land plants; as in the hairs upon the leaf- 
stalks of the common groundsel; but these do not show it 
so well, nor are they so easily managed as the preceding. 
Many microscopists who are not fortunate enough to be 
in the neighbourhood of these plants (indeed the Vallisneria 
is a foreign one) grow them in jars; so afew remarks as to 
the treatment they require will not be out of place. The 
Vallisneria requires a temperature not lower than 55° or 
60°, and even a higher degree than this renders its growth 
quicker; and no great change must take place: the more 
equable the temperature the more healthy will the plant be. 
A glass jar should be taken, having an inch or two of mould 
at the bottom, which must be pressed down closely, and the 
plant must be set in this. Water must then be gently 
poured in, so as not to disturb the mould. As this plant 
flourishes best when the water is frequently changed, 
Mr. Quekett recommends that the jar should be occasionally 
placed under a tap of water, and a very gentle stream 
allowed to fall into it for several hours, by which means 
much of the confervoid growth will be removed and the 
plant invigorated. The Anacharis may be rooted in the 
earth like the Vallisneria, but a small detached piece may be 
thrown into the jar of water and there left until wanted. 
For months the circulation will be well shown by it, and it will. 
probably grow and increase. It is also very healthy in an 
