THE VEGETABLE CELL. 14*1 



from one another in liygroscopical respects, a g., in the elaters of Equise- 

 tum, the peristome of the Mos&es, &c. The cause of these motions is 

 usually so conbpicuous, and the proof that they result from desiccation so 

 readily shewn, since wetting the dried organ brings it hack into its old 

 form, that the cause has but rarely been misconceived^ and such motions 

 ascribed to a vital force, irritability, &c., in the way Purkinje so strangely 

 did, in regard to the opening of the anthers, in a special work {'' De 

 cellulis aQitheraTmn fibrosis^'' 1830). 



Passing to the movements of living plants, we meet first, as 

 one of the most mysterious phenomena, the locomotion of many 

 lower aquatic Algse, the Diatomacese, Desmidiacese, and Oscilla- 

 torie^, which, on account of this, have been so frequently re- 

 garded as animals. In the Diatomacese and Desmidiacese, the 

 motion consists of a slow waving backwards and forwards in the 

 direction of their longitudinal diameter, during which no change 

 of form, such as curvatu.re or the like (which indeed would be im- 

 possible in the Diatomacese, on account of their siliceous loriea), 

 can be observed in the cell constituting the plant. Neither can 

 special organs of motion (such as cili^) be discovered, and Ehren- 

 berg's idea that he detected a moveable foot, similar to that of 

 the MoUusca, must be attributed decidedly to erroneous observa- 

 tion. 



The organic process upon which this motion depends is alto- 

 gether uninvestigated. Nageli ('' Oattungen der einzelUger 

 Algen" 20) explains the motion by supposing, that in the absorp- 

 tion and excretion of fluid matters connected with the nutrient 

 processes of these plants, the attraction and repulsion of the fluids 

 are irregularly distributed over the portions of the surface, and 

 that these currents are so active as to overcome the resistance of 

 the water ; but this explanation is devoid of any positive basis. 

 The external circumstances in which the plants are placed have 

 influence over the motion so far, that when the little plants lie 

 hidden in mud, they rise up to its surface if the sun shines upon 

 it, and they hury themselves in the mud when its surface be- 

 comes dried up (RaWs, ''British Desmidem/' 20). 



The motion which presents itself in the Oscillatorice is more 

 complicated, since not only does the entire plant move backwards 

 and forwards like a little rod, but a pendulous swinging of the 

 filaments to and fro occurs, together with a curvature in a 

 spiral direction (See Kiitzing, ''Phycol Generalis" 181 ; Frese- 

 nius, '' IFeheT Ba% and Lehen der Omllarien,'' in the Museum Sen- 

 Icenhergianum, iii. 284). This curvature deserves our attention in 

 a higher degi'ee, that these plants are composed of a simple row of 

 flattened cells enclosed in a membranous sheath. Under these 

 circumstanees, a curvatxire of the filament cannot depend (as in 

 the higher plants) upon a different relative contraction or expan- 

 sion of difi'erent cells lying side by side, but must arise from a 

 diff'erent behaviour of the difl'erent lateral surfaces of the two side 



