132 MOVEMENTS IN CELLS. ROTATION. 



275. Special Movements of Fluids. Besides this general circulation 

 of the sap, special movements have been observed in the cells of 

 plants, which have been included under the name of Rotation (rota, a 

 wheel), or Gyration (gyms, a circuit or circle). These motions have 

 been detected in the cells of many aquatic plants, especially species of 

 Chara and Vallisneria, and in the hairs of Tradescantia. The currents 

 proceed in a more or less spiral direction, and are rendered visible 

 by the granules of chlorophylle which they carry along with them. 

 There exist also other granules in the fluids, which are coloured 

 yellow by iodine, and are probably of a nitrogenous nature. 



276. The species of Chara, in which rotation has been observed, 

 are aquatic plants growing in stagnant ponds, and are composed of a 

 series of cylindrical cells, placed end to end. Sometimes the plant con- 

 sists of a single central cell ; at other times there are several smaller 

 ones surrounding it, which require to be scraped off in order to see 

 the movements. Many of the species are incrusted with calcareous 

 matter, so as become opaque, while others, as Chara flexilis, included 

 under the division Nitella, have no incrustation, and are transparent. 

 In these plants the movements take place between the two membranes 

 of which the cell- wall is composed. Some granules, of a green colour, 

 are attached to the cell- wall, while others are carried with the current, 

 which passes along one side and returns by the other, following an 

 elongated spiral direction. The descending current in the branches 

 is next to the axis. 



277. In Vallisneria spiralis (which includes V. Micheliana and 

 Jacquiniana), the cells in all parts of the plant, as in the leaf, root, 

 flower-stalk, and calyx, contain numerous green granules, and an 

 occasional cytoblast or nucleus, which, under certain circumstances, 

 are carried, with the juices of the plant, in continual revolution round 

 the walls of each cell. Although in different cells the currents pro- 

 ceed often in different directions, still, in any given cell the rotation is 

 uniform; for if stopped by cold it resumes the same direction. Rota- 

 tion 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 microscope. The part is to be viewed in 

 water, between two pieces of glass ; and a little heat is sometimes use- 

 ful in causing the movements to commence. 



278. A similar intra-cellular circulation, is seen in species of Potamo- 

 geton, Hydrocharis, and many aquatics, as well as in the moniliform 

 purple hairs on the filaments, and in the calycine hairs of Trade- 

 scantia virginica. In the examination of these hairs a higher micro- 

 scopic power is required than in the case of the plants previously 



