4 INTRODUCTION 



induce streaming, which is then independent of the action of light. The 

 same author distinguishes between the primary streaming which occurs as 

 a normal phenomenon in certain plants or parts of plants, and the secondary 

 streaming produced by mechanical, chemical, or physical stimuli in pre- 

 viously quiescent cells. These distinctions are purely artificial ones, for 

 in certain cases the ' primary ' streaming may cease, and yet the cell may 

 remain capable of exhibiting 'secondary' streaming when stimulated. 

 Hauptfleisch also erroneously states that mechanical stimuli, if they do 

 not cause death, do not stop streaming, whereas as we shall see later 

 a temporary stoppage is readily induced by various mechanical stimuli 

 which produce no permanently injurious effect. 



As regards the influence of external agencies upon streaming a very 

 large amount of work has been done, the results of which are in many 

 cases contradictory. This is especially the case in respect to the action 

 of carbon dioxide, oxygen, and other gases, the discordant results 

 obtained by different investigators being in certain cases due to specific 

 differences between the physiological properties of the plants employed, 

 and in other cases being due to experimental errors or the use of impure 

 gases \ 



Concerning the physics of streaming movements little is known, nor 

 has any attempt been made to determine even approximately the amount 

 of work done by the streaming protoplasm of a closed cell in overcoming 

 the friction and cohesion between its rotating and stationary layers. If 

 the amount of energy expended could be directly estimated it would be 

 easy to find relative values for the other factors in the equation, but 

 unfortunately the energy produced by respiration is never wholly employed 

 in the production of movement. The difficulties in the way of direct 

 experimental research are therefore very great, but by various methods 

 which will be described later it is possible to obtain approximate estima- 

 tions of the forces at work and the resistance offered to their action. 



It is only in very few cases that streaming persists during the entire 

 existence of the adult cell, and that it is so closely connected with the 

 vitality of the latter that permanent cessation always indicates a fatal 

 injury (Char a, Nitella^ and the cells of a few Phanerogams). In most cases 

 streaming is a more or less transitory phenomenon, and is frequently 

 induced by external stimuli, chemical, physical, or mechanical. Thus when 

 a leaf of Elodea is torn off, after a short latent period streaming appears 

 at the base of the leaf near the point of injury, and later in successive 

 regions spreading away from it. Now Richards 2 has shown that when 



1 The literature will be given in detail subsequently. On carbon dioxide cf. Kabsch, Bot. Zeitg., 

 1862, p. 340; Stich, Flora, 1891, XLIX, p. i; Frankel, Zeitschr. f. Hygiene, 1889, Ed". V, p. 332 ; 

 Arsonval, Compt. rend., 1891, T. cxil, p. 667. 



2 Ann. of Bot., 1896, Vol. X, p. 531. 



