364 STRUCTUKB OF PHANEKOGAMIC PLANTS. 



of this country; it may, however, be readily grown in a tall 

 glass jar having at the bottom a couple of inches of mould, 

 which, after the roots have been inserted into it, should be 

 closely pressed down, the jar being then filled with water, of 

 which a portion should be occasionally changed.^ The jar should 

 be freely exposed to light, and should be kept in as warm but 

 equal 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 M'ith a sharp knife. 

 If this be taken from the surface, so that the section chiefly con- 

 sists of the superficial layer of cells, these will be found to be 

 small, and the particles of chlorophyll, though in great abun- 

 dance, will rarely be seen in motion. But if, after the removal 

 of this layer, a deeper stratum be sliced off, this will be found to 

 consist 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 favorable 

 circumstances, in the separated fragment, for a period of weeks 

 or even of montbs. Hence when it is desired to exhibit the 

 phenomenon, the preferable method is to make 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 

 i-eceive 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.^ 

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

 accidentally introduced into this country about twelve years ago, 

 has since spread itself with such rapidity through our canals and 

 rivers, as, in many instances, seriously to impede the 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 suflicient for the origination of new 

 plants. The leaves have no distinct cuticle, but ai'e for the most 

 part composed of two layers of cells, and these are elongated 

 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 



' Mr. Qnekett has found it the most convenient method of changing the water in the 

 jars in which Chara, Vallisneria, &c., are growing, to place them occasionally 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 3 id of 



^ An object-glass of ^-di inch focus affords the best power for the observation of this 

 interesting j)henomenori. 



