ROTATION. 



[ 555 ] 



ROTATION. 



shifts in the latter type, as in the former, 

 the two kinds are scarcely definitely distin- 

 guishable. They may, however, be spoken 

 of separately. 



The rotation in Chara (and Nitella) has 

 been long known ; a similar movement oc- 

 curs in many water-plants, such as Vallis- 

 neria, Hydrocharis, Anacharis, Stratiotes, 

 Sagittaria, Potamogeton, Ceratophyllum, &c., 

 where it is seen best in the more delicate 

 foliaceous structures, such as young leaves, 

 stipules, or sepals, or in the young rootlets ; 

 it has also been observed in the fruit-stalks of 

 Blasia pusilla, and some other Hepaticaceae. 

 The general rotation has not yet been ob- 

 served in any land-plants. 



In the Characese the wall of the cells is 

 lined with chlorophyll-granules, leaving two 

 oblique or spiral striae bare (fig. 129, p. 134) ; 

 these striae indicate the boundaries of the 

 ascending and descending currents (marked 

 by arrows). The moving substance is a vis- 

 cid semifluid layer lying within the chloro- 

 phyll-layer, and itself surrounding the watery 

 cell-sap occupying the centre of the cell. 

 This layer, forming a kind of gelatinous sac, 

 moves in a spiral course up one side of the 

 cell and down the other, the motion being 

 rendered very evident by chlorophyll- and 

 other granules imbedded in it ; these appear 

 to be carried along passively by the stream, 

 the larger slowly, the smaller with greater 

 rapidity. In Vallisneria, Anacharis, &c. 

 the chlorophyll-granules and the nucleus 

 are imbedded in and moved with the flowing 

 protoplasm. If long cells of Chara are bent 

 or tied round by a ligature, the circulation 

 is not stopped, but takes place independently 

 in each half. If a cell of Chara is cut across, 

 the protoplasm of the current flowing to- 

 wards the cut surface escapes at once, but 

 that of the current flowing away, goes on to 

 the end of the cell, turns round, and then 

 flows towards and out from the wound. 



The size of the stream seems to be in in- 

 verse proportion to the length of the cell, 

 decreasing as the latter acquires its full de- 

 velopment. The rapidity of the current 

 varies according to the age of the plant and 

 the activity of its vegetation. It is most 

 rapid in hot weather and in sunshine. Arti- 

 ficial elevation of temperature in the water 

 in which the plant grows, up to a certain 

 point, hastens the movement; a heat above 

 80 Fahr., however, retards it for a time. 

 A temperature of 1 12 Fahr. kills the plant, 

 as also does a cold of about 20. Darkness 

 appears merely to exert effect through its 



influence on the activity of the vegetation. 

 Keeping Chara in water exhausted of air 

 does not stop the rotation until the plant 

 dies. Most chemical reagents seem to exert 

 no special action ; only lime-water appears 

 to stop it in a few moments. A solution of 

 sugar or gum, or milk greatly hastens the 

 rotation inVallisneria,soihsit the protoplasm 

 is moved on in waves ; but the primordial 

 utricle finally dissolves, and the movement 

 ceases. Passing an electric current through 

 the cell stops the current for a time, but it 

 recovers itself, just as occurs after any me- 

 chanical interference. If several cells are 

 injured by cutting or pricking, the whole 

 rotation stops in young plants, but it gra- 

 dually returns as before in the uninjured 

 cells. Pressure interrupts or stops the mo- 

 tion for a time only; when removed, the 

 current is gradually restored; but actual 

 injury to the cell stops it for ever. 



The rotation which takes place between 

 the external surface of the green layer and 

 the outer cell-membrane in Closterium and 

 other DESMIDIACE^J appears to be of the 

 same kind as the above. 



The circulation in reticular currents, first 

 observed by Mr. Brown in the hairs of the 

 stamens of Tradescantia, appears to exist 

 far more extensively, if it be not even a uni- 

 versal phenomenon. It has been observed 

 in the Confervoideae, Fucoideae, Florideae, 

 Lichens, Fungi, Hepaticae, Equisetaceae, 

 Lycopodiaceae, and Ferns, and in the most 

 varied families of Flowering plants. It is 

 seen most easily in young tissues, especially 

 such as can be prepared readily without 

 much mechanical injury; for example, in 

 hairs, cells of the pulp of fruits, cells of the 

 germen of Onagraceae, of the labellum of Or- 

 chids, &c. It generally exhibits the follow- 

 ing characters : in the middle or at one side 

 of the cell occurs a large heap of protoplasm, 

 in which is imbedded the nucleus ; from this 

 protoplasm more or less slender filaments 

 run out over the cavity of the cell, and as 

 these contain numerous fine granules, a 

 flowing movement which takes place becomes 

 evident by the change of place of the gra- 

 nules. Attentive examination shows that 

 these flow out from the central mass, and 

 return to it ; and moreover, that the currents 

 change their form and direction; and lastly, 

 that the nucleus itself moves. This rotation 

 cannot be observed in very young cells when 

 the cavity is densely filled with protoplasm; 

 but Hofmeister states that he has seen the 

 entire primordial utricle rotate in the special 



