DEVELOPMENT OF CELLS. — CYCLOSIS. 391 



toplasmic mass, analogous to that of which we have seen persistent 

 representations among the simplest Protophytes (§§ 183-187). 

 Thus it has been usually held that every Leaf has its origin in a 

 certain cell of the Axis, which rapidly multiplies itself so as to form 

 a minute protuberance that gradually takes the foliaceous form ; 

 and that the subsequent extension of this is due to a continuance 

 of the same process. The observations of Mr. Wenham, * however, 

 afford strong reason for the belief that in some cases, at any rate, 

 the leaf originates in a layer of Protoplasm (Fig. 201), which is 

 in the first instance homogeneous, but in which large vacuoles, 

 disposed with a certain degree of regularity, soon make their ap- 

 pearance ; those vacuoles become the cavities of the first cells, 

 whilst the plasma between them, acquiring increased consistence, 

 is converted into the walls of these cells. Sometimes, when one 

 of the first-formed vacuoles is unusually large, it is divided into 

 two by the extension of a bridge of protoplasm across it ; on the 

 other hand, if the plasmatic division between the vacuoles should 

 be unusually broad, a new vacuole forms in its substance ; and 

 thus is formed a congeries of cells having a certain average size 

 and shape, which, when matured, begin to multiply by self -division, 

 and gradually evolve themselves into the perfect leaf. 



287. 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 Characece (§ 254), aud 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 move- 

 ment of the particles which the current carries along with it. 

 The best examples of it are found among submerged Plants, in 

 the cells of which it continues for a much longer period than it 

 usually does elsewhere ; and among these are two, the Vattisneria 

 spiralis and the Anacharis alsinastrum, which are peculiarly 

 fitted for the exhibition of this interesting phenomenon. — The 

 Vattisneria 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 occasionally 

 changed, f The jar should be freely exposed to light, and should 

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



* "Transactions of the Microscopical Society," N.S., Vol. iv. (1856 , 

 pp. 1 and 60. See also the observations of Mr. Davey, at p. 100, and 

 those of the Rev. S. G. Osborne, at p. 104, of the same Volume. 



t Mr. Quekett 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 rid of. 



