134 PREPARATION AND MOUNTING 



tion, however, 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 unusually obstinate the warmth 

 may be slightly increased, but too great heat destroys the move- 

 ment 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 a slide. The Ana- 

 cbaris alsinastrum is one of these : it grows in water, having 

 three leaves round the stem, then a bare portion, again another 

 three leaves, and so on. 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 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 Cham vulgaris and two 

 or three of the Nitellse, &c., this phenomenon may also be seen 

 with no preparation except plucking a part from the stem and 

 laying it upon 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 above. 



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 a few remarks as to the treatment they 



