FUNCTION.] XATURE OF ROTATION. 333 



In the cells of Hydrocharis Morsus-Rance the fluid has been 

 observed to move round and round their sides in a rotatory 

 manner, which, however, has not been seen to follow any 

 particular law. 



Pouchet and Meyen (An. Sc., n. s., iv. 257.) have remarked 

 it in the longer cells of the stem of Zannichellia palustris, and 

 the latter in Vallisneria, Stratiotes, Potamogeton, and the 

 radical hairs of Marchantia. It may be distinctly seen in 

 Equisetum. According to Schultz (Arch. Bot. ii. 425.), it is 

 also visible in Podostemads, Ceratophyllum, Naiads, Sea- 

 wracks, Lemna, Mosses, Liverworts, Lichens, Algals, and 

 Fungals. The rotation in Vallisneria canadensis is most 

 beautiful. In large cylindrical cells filled with a transparent 

 fluid, there float large brilliantly green spherules, which 

 rotate up one side and down another with a slow motion, 

 sometimes crowding together, sometimes distant, and occa- 

 sionally stopping. There is, moreover, among the woody 

 tubes, a more rapid movement of very minute oval bodies, 

 which goes on in lines upwards and downwards. 



According to Meyen, the granules seen moving in the 

 rotating currents are of different kinds (Ann. Sc., n. s. iv. 

 261.), the larger being grains of starch, others vesicles slightly 

 coloured by chlorophyll, and some being drops of oil. I find 

 but little trace of fsecula in Vallisneria, tincture of iodine 

 chiefly producing a brown colour upon the granules, but here 

 and there a blue centre was visible. 



By no one have the phenomena of rotation been described 

 with more accuracy than by Professor Mohl. " When the 

 protoplasm," he says, " has assumed the form of filaments, 

 a current may almost always be observed in them. This 

 may, of course, be easily detected when readily perceptible 

 globules are contained in the currents, as in the filamentary 

 hairs of Tradescantia, in the stinging hairs of Urtica, in the 

 hairs of the Melon, &c. ; but where, on the contrary, this is 

 not the case, and the filaments consist of a very homogeneous 

 transparent mass, as for instance, in the hairs of Alsine media, 

 the existence of the current can only be inferred from the 

 change of position in the filaments, With respect to this 

 alteration in the position of the currents, the cessation of 



