MOVEMENTS IN CELLS — ROTATION. 



153 



quiniana), the cells in all parts of the plant, leaf, root, flower-stalk, 

 and calyx, contain numerous green granules, and an occasional cyto- 

 blast or nucleus, which, under certain circumstances, are carried, with 

 the juices of the plant, in continual revolution round the walls of each 

 cell (fig. 245). Although in different cells the currents proceed often 

 in different directions, still in any given cell the rotation is uniform ; 

 for if stopped by cold it resumes the same direction. Eotation will 

 continue in detached portions of the plant for several days, or even 

 for three or four weeks. The best way of showing these motions is to 

 take a small portion of a young leaf and divide it in halves, by making 

 a very oblique section on the plane of the leaf, by which means a 

 transparent end is obtained. This should be done at least an hour 

 before it is put under the micro- 

 scope. The part is to be viewed 

 in water, between two pieces of 

 glass ; and a little heat is some- 

 times useful in promoting the 

 movements. In Vallisneria the 

 motion ceases at about 45° 

 Fahr., while in Chara it goes 

 on at a lower temperature ; if 

 the temperature be raised above 

 150° the motion ceases. 



A similar intracellular cir- 

 culation is seen in species of 

 Potamogeton, Hydrocharis, and 

 Anacharis, as well as in the 

 moniliform purple hairs on the 

 filaments, and in the calycine 

 hairs, of Tradescantia yirginica. 

 In the examination of these 

 hairs a higher microscopic power 

 is required than in the case of 

 the plants previously mentioned. 

 A nucleus is usually seen in the 

 cells of these hairs, and it may 

 either remain immovable, or 

 may be carried along with the 

 current. The movements ap- 

 pear to be confined between a 

 double cell-wall. Fig. 246 shows 

 a calycine hair, p, of Tradescantia virginica, with a small portion of 



Kg. 246. 



Fig. 246. Hair, f, taken from the calyx of Tradescantia virginica, with a small portion of 

 the epidermis, e c, on which there Is a stoma, s. In each of the epidermal cells there is a 

 nucleus, %, and currents (rotation), the direction of which is indicated by the arrows. 



