356 



THE MICROSCOPE AND ITS REVELATIONS. 



phyllus) or the London Pride (Saxifraga crassi folia). Such, cells usually 

 contain evident nuclei, which are turned brownish-yellow by iodine, 

 whilst their membrane is only turned pale-yellow; and in this way the 

 nucleus may be brought into view, when, as often happens, it is not 

 previously distinguishable. If a drop of the iodized solution of chloride 

 of zinc be subsequently added, the cell-membrane becomes of a beautiful 

 blue color, whilst the nucleus and the granular protoplasm that surrounds 

 it retain their brownish-yellow tint. The use of dilute nitric or sulphuric 

 acid, of alcohol, of syrup, or of several other reagents, serves to bring 

 into view the primordial utricle ( 223); its contents being made to- 

 coagulate and shrink, so that it detaches itself from the cellulose wall 

 with which it is ordinarily in contact, and shrivels up within its cavity, 

 as shown in Fig. 235. It would be a mistake, however, to regard this as 

 a distinct membrane; for it is nothing else than the peripheral layer of 

 protoplasm, naturally somewhat more dense than that which it includes,, 

 but deriving its special consistence from the operations of reagents. 



* 10.239. 



Successive stages of Cell-formation in the development of the Leaves of Anacharis alsinas- 

 trum: A, growing point of the branch, consisting or a protoplasmic mass with young cells, the 

 projections at its base being the rudiments of leaves; B, portion of one of these incipient leaves in 

 a more advanced condition: c, the same in a still later stage of development. 



353. It is probable that all Cells, at some stage or other of their 

 growth, exhibit, in a greater or less degree of intensity, that curious 

 movement of cyclosis, which has been already described as occurring in 

 the CharacecB (* 258), and which consists in the steady flow of one or of 

 several currents of protoplasm over the inner wall of the cell; this being 

 rendered apparent by the movement of the particles which the current 

 carries along with it. The best examples of it are found among sub- 

 merged plants, in the cells of which it continues for a much longer 

 period than it usually does elsewhere; and among these are two, the 

 Vallisneria spiralis and the Anacharis alsinastrum, which are peculiarly* 

 fitted for the exhibition of this interesting phenomenon. The Vallisne- 

 ria is an aquatic plant that grows abundantly in the rivers of the south 

 of Europe, but is not a native 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 



