ON THE POWER OF MOVEMENT IN PLANTS. 145 



thought to be, a movement of the watery cell-sap ; it is that of the 

 protoplasm making paths for itself in the cell-sap. 



It may be seen in many plant-cells ; notably in the Stoneworts, 

 Nitella and Chara. In Chara it is the inner layer of protoplasm 

 that rotates, carrying the nucleus with it, while the outer layer, or 

 'primordial utricle,' as it is called, immediately \^ithin the cell- 

 wall remains motionless, as do also the chlorophyll grains. The 

 motion in Chara is at an angle with the wall, not parallel to 

 it. In Vallisnerta, on the other hand, it goes on parallel to 

 and all round the wall carrying the chlorophyll grains with it. 

 It is beautifully seen in the bristles on the ovary of Circcea, the 

 Enchanter's Nightshade. Cold retards it. Heat accelerates it. 

 Electrical currents stop it, but it instantly sets off again on 

 breaking the current. Jolting the cell, or pricking it, also stops it. 

 Speed varies : in Circcea bristles, which are about half a ' line ' long, 

 it completes the round in about one minute ; in ValUsneria it 

 moves at the rate of the one-hundred-and-eightieth part of a line 

 per second ; sometimes in this plant much faster. 



II. — Cirailation, where the protoplasm is hollowed out and 

 the motion is in net-like currefifs radiating from and returning to 

 the nucleus, passing in threads and bands through the cell-sap. 



This is seen in the cells of the purple hairs of Tradescantia 

 (Spider-wort), in the cells of Celandine, in Nettle-hairs, and in 

 many others. Here the movement is less regular and more 

 spasmodic, now advancing, now retreating, now ceasing, now 

 recommencing. The hairs on the buds of Althcea^ the Marsh 

 Mallow, show it exceedingly well. 



The cause of these movements is still a subject for investiga- 

 tion. Endless theories have been and are being advanced, and 

 held most pertinaciously by some observers, who think they can 

 cry * Eureka^ and put an end to all further discussion. Generally 

 speaking, we may write down the following as among the causes 

 of movements inside cells : — 



Constant Chemical Changes^ such as the formation and evo- 

 lution of carbonic acid, the formation of starch and the albumi- 

 noids ; these cause successive changes in the equilibrium of forces 

 and produce heat, and probably also electrical currents. These in 

 turn give rise to forces of astounding magnitude, setting atoms and 



