392 CYCLOSIS IN VALLISNERIA AND ANACHARIS. 



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 superficial 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 rotation takes 

 place, in contiguous cells, in opposite directions. If the movement 

 (as is generally the case) be checked by the shock of the operation, 

 it will be revived again by a gentle warmth ; and it may continue 

 under favourable circumstances, in the separated fragment, for a 

 period of weeks, or even of months. Hence, when it is desired to 

 exhibit the phenomenon, the preferable 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 

 Object-glass of l-4th inch focus will serve for the observation of 

 this interesting phenomenon, and very little more can be seen with 

 a l-8th inch Objective ; but the l-25th inch lately constructed by 

 Messrs. Powell and Lealand enables the borders of the Proto- 

 plasmic current that carries along the particles of Chlorophyll to 

 be distinctly defined ; and this beautiful phenomenon may be 

 most luxuriously watched under their Patent Binocular (§ 62). 



288. The Anacharis alsinastruni 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 elongated and 

 colourless 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 exa- 

 mination of the Cyclosis in Chara or in Yallisneria ; the l-8th inch 



