72 THE CELL 



Chara contains no chlorophyll corpuscles, but only nuclei and 

 granules. The protoplasm of the inner layer, which, compared 

 to that of the outer layer, appears to be richer in water, exhibits 

 rotatory streaming movements, which take place in the following 

 manner. The current passes up along the longitudinal wall of an 

 elongated cell, then, turning round past a transverse wall, flows 

 down the opposite longitudinal side, until, curving round again 

 at the second transverse wall, it reaches the starting point, 

 when the cycle recommences. Between the upward and downward 

 streams there is a more or less broad neutral strip where the protoplasm 

 is at rest, and where as a rule it is reduced to a very thin layer. 

 In Nitella there are no chlorophyll corpuscles along this neutral 

 strip in the outer layer. 



A connecting link between the rotatory movement and true 

 circulation is afforded us by the so-called "fountain-like rotation" 

 (Klebs III. 14). This, which as a rule but rarely occurs, is 

 found in young endosperm cells of' Ceratophyllum, in young wood 

 vessels of the leaf-stem of Ricinus, etc., etc. Here the protoplasm, 

 in addition to spreading itself out in a thick layer over the inner 

 surface of the cellulose wall, stretches itself in the form of a 

 thick central strand along the longitudinal sap-cavity of the cell. 

 Under these circumstances a single stream flows along this central 

 strand, spreading itself out in all directions like a fountain upon 

 the transverse wall, upon which it impinges ; then streaming 

 down the sides of the cell, it collects again at the opposite trans- 

 verse wall, where it re-enters the main axial stream. 



The motion which is described as circulation is observed in 

 those plant and animal cells in which the protoplasm spreads 

 itself out, both as a thin layer beneath the membrane, and also in 

 the form of more or less delicate threads, which traverse the 

 sap-cavity and are united together to form a net-like structure. 



The objects which have been most examined are the staminal 

 hairs of the various kinds of Tradescantia, and young hairs of the 

 stinging nettle, and of pumpkin shoots. 



The phenomenon of circulation resembles that observed in the 

 protoplasmic nets of Myxomycetes, and of the delicate pseudo- 

 podia of the Rhizopoda. Circulation consists of two kinds of 

 movements. In the first place attention must be drawn to the 

 streaming movements of the granules. In the thinnest threads 

 they move more or less quickly over the surface of the walls in one 

 direction, whilst in broader bands several separate streams may 



