MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 357 



occasionally changed. ' The jar should be freely exposed to light, and 

 should be kept in as warm but equable a temperature as possible. The 

 long grass-like leaves of this plant are too thick to allow the transmission 

 of sufficient light through them for the purpose of this observation; and 

 it is requisite to make a thin slice or shaving with a sharp knife. If this 

 be taken from the surface, so that the section chiefly consists of the super- 

 ficial layer of cells, these will be found to be small, and the particles of 

 chlorophyll, though in great abundance, will rarely be seen in motion. 

 This layer should therefore be sliced off (or, perhaps still better, scraped 

 away) so as to bring into view the deeper layer, which consists of larger 

 cells, some of them greatly elongated, with particles of chlorophyll in 

 smaller number, but carried along in active rotation by the current of 

 protoplasm; and it will often be noticed that the directions of the rota- 

 tion in contiguous cells are opposite. If the movement (as is generally 

 the case) be checked by the shock of the operation, it will be revived 

 again by gentle warmth; and it may continue under favorable circum- 

 stances, in the separated fragment, for a period of weeks, or even of 

 months. Hence, when it is desired to exhibit the phenomenon, the pre- 

 ferable method is to prepare the sections a little time before they are 

 likely to be wanted, and to carry them in a small vial of water in the 

 waistcoat pocket, so that they may receive the gentle and continuous 

 warmth of the body. In summer, when the plant is in its most vigorous 

 state of growth, the section may be taken from any one of the leaves; but 

 in winter, it is preferable to select those which are a little yellow. An 

 Objective of l-4th inch focus will serve for the observation of this inter- 

 esting phenomenon, and very little more can be seen with a l-8th inch; 

 but the l-25th inch constructed by Messrs. Powell and Lealand enables 

 J ~he borders of the protoplasmic current, which carries along the particles 

 of chlorophyll, to be distinctly defined; and this beautiful phenomenon 

 may be most luxuriously watched under their patent Binocular ( 81). 



354. The Anacharis alsinastrum is a water-weed, which, having been 

 accidentally introduced into this country several years ago, has since 

 spread itself with such rapidity through our canals and rivers, as in many 

 instances seriously to impede their navigation. It does not require to 

 root itself in the bottom, but floats in any part of the water it inhabits; 

 and it is so tenacious of life, that even small fragments are sufficient for 

 the origination of new plants. The leaves have no distinct cuticle, but 

 are for the most part composed of two layers of cells, and these are elon- 

 gated and colorless in the centre, forming a kind of midrib; towards the 

 margins of the leaves, however, there is but a single layer. Hence no 

 preparation whatever is required for the exhibition of this interesting 

 phenomenon; all that is necessary being to take a leaf from the stem (one 

 of the older yellowish leaves being preferable), and to place it with a 

 drop of water, either in the Aquatic-box, or on a slip of glass beneath a 

 thin-glass cover. A higher magnifying power is required, however, than 

 that which suffices for the examination of the cyclosis in Chara or in Val- 

 lisneria; the l-8th inch Object-glass being here preferable to the l-4th, 

 and the assistance of the Achromatic Condenser being desirable. With 



1 Mr. Quekett found it the most convenient method of changing the water in 

 the jars in which Chara, Vallisneria, etc. , are growing, to place them occasion- 

 ally under a water-tap, and allow a very gentle stream to fall into them for some 

 hours; for by the prolonged overflow thus occasioned, all the impure water, with 

 the Conferva that is apt to grow on the sides of the vessel, may be readily got rid 

 of. 



