OF THE ELEMENTARY STKUCTUEES. 



737 



Fig. 1106. 



n 



"V 



served, by filling a bladder with coloured syrup, attacliing to 

 its opeu end a glass tube, and then immersing it in a vessel 

 containing water {fig. 1106). Under 

 such circumstances, the volume of the 

 denser fluid in the interior of the blad- 

 der becomes increased (as may be at 

 once seen by its rise in the tube), by 

 the more rapid passage through the 

 membrane of the thinner fluid than of 

 the thicker, though at the same time a 

 less portion of the syrup passes out into 

 the water or thinner fluid, as may be 

 proved by the sweet taste and colour 

 which the latter gradually acquires. 

 This double current will continue as 

 long as there is any material difference 

 of density between the two liquids. The 

 stronger in-going current is termed endos- 

 mose, and the weaker out-going current, 

 exosmose. If the position of the liquids 

 be reversed, the currents will be reversed 

 in like manner, the preponderating cur- 

 rent, in almost all cases, being that 

 which sets from the thinner to the 



denser liquid. pig^ iioe. Apparatus to show 



The absorption and transmission of endosmose^ud exosmose it 

 T . 1 ^i 1 1 11 • consists of a ttladder fllled 



liquid matters through cells is now very with syrup, to the open end 

 easy to explain, for as the fluid contents of which a tube is attached, 

 ^ "1, 1, « ,1 , p 1 ^ and the whole placed ma 



01 the cells oi the roots or plants are vessel coutainiug water. 



denser than the water contained in the 



media in which they grow, they will continually absorb the 

 latter by endosmose (see Absorption) ; and as the changes which 

 are going on in the cells by evaporation, assimilation, and other 

 processes on the surface of plants tend to thicken their contained 

 liquids, there will also be a constant passage of the absorbed 

 fluids from cell to cell towards those parts where such processes 

 are taking place. The laws of ordinary adhesive or capillary 

 attraction and of the diffusioji of fluids also regulate the flow of 

 the juices, which in certain cases may be even set in motion by 

 either force. The action, however, of the intervening mem- 

 brane (cell-wall), in greatly modifying or even overcomme: os- 

 motic action, is evidenced by the numerous cases in which 

 neighbouring cells contain different substances without their 

 intermixture. 



3. Movements in the Contents of Cells. — In many cells, and 



probably in all at a particular period of their life, when they 



are in a vitally active state, a kind of movement or rotation 



of a portion of their contents takes place. This movement 



3 B 



