154 MOVEMENTS IN CELLS — ROTATION. 



the epidermis, e e, on which a stoma, s, is seen. In each of the 

 cells, both of the epidermis and the hair, there is a nucleus, n, 

 and rotatory currents, the direction of which is indicated by the 

 arrows. In each cell, as seen at a, there are several currents, which 

 cross each other at the point where the nucleus is situated, thus 

 giving rise to the appearance of an irregular network. The hairs 

 of many other flowering plants exhibit rotation (fig. 90), and it is 

 probable that in all young cells these currents may be observed. 

 The circulating fluid is a mucilaginous protoplasm or formative matter, 

 and in Ohara and Vallisneria it forms a uniformly investing layer on 

 the inner surface of the cell. The motions would appear to be 

 connected in some way with the nutrition of cells and the formation 

 of new ones ; and while they continue throughout life in aquatics, 

 they often cease in plants living in air, after they have attained a 

 certain development. Mohl's experiments have shown that at the 

 temperature of 66° Fahrenheit the quickest motion was l-125thofa 

 Parisian line,* the slowest, l-600th, and the mean, I-185th. 



Schleiden says that in the Vallisneria cells it is not the ceU-sap 

 that is in motion, but a mucilaginous fluid, with which the chloro- 

 phyll granules and the nucleus are connected, and which flows in an 

 uninterrupted manner along the cell-waUs. In Ohara, also, he states 

 it is not the cell-sap which moves, but a denser fluid, present in large 

 quantity, and occupying the outer part of the cell cavity. Mohl 

 thinks that a homogeneous protoplasm fills these cells at first com- 

 pletely, but that during growth it becomes hollowed out into one or 

 more cavities, and that around these the mucilaginous matter 

 circulates. 



The velocity of the currents in various plants, at 66° to 68° 

 Fahrenheit, is thus given by Mohl : — 



Filamental hairs of Tradescantia virginica, — j^ to -^-^ of a Parisian line in a 



second ; mean, -^^. 

 Leaves of Vallisneria spiralis — quickest, x^ ; slowest, -^ ; mean, -rir j of * 



line in a second. 

 Stinging hairs of Urtioa haccifera — quickest, -^^ ; slowest, -^^ ; mean, yitt- 

 Cellular tissue of young shoot of Sagittaria sagittifolia, y^ to tAt j mean, r^. 



„ „ leaf of do., yttit to Tsm ; mesca, j^. 



Hairs of Cuourhita Pepo — quickest, yfj ; slowest, ^p^ ; mean, xAy 



The measurements were made by noting the passage of the globules 

 across the field of a micrometer, fixed in the ocular of the microscope, 

 and counting the strokes of a seconds pendulum. These movements 

 appear more rapid to the observer ; but then it must be recollected 

 that the parts are seen in a highly magnified state. 



The cause of those intracellular movements is obscure ; both vital 



* Parisian line = 'OSSSIS of an inch, 



