76 PHYSIOLOGY OF STREAMING MOVEMENTS 



threads. In the latter case the subsequent transmission of the stimulus 

 must be vital, but might be the result of continued diffusion in the 

 former case. 



SECTION 31. The Action of Nutrient Substances. 



Food-materials. Cells completely packed with solid food- materials 

 never exhibit any perceptible streaming movements, and even if a tendency 

 to streaming existed the mechanical inertia of the entire mass might be 

 too great to be overcome by any propulsive force exerted by the relatively 

 small protoplasmic portion. Streaming, however, often commences as 

 the food-materials are removed. For example, streaming begins in the 

 etiolated amyliferous winter-shoots of Elodea * after they have been kept 

 for some days in well-aerated water at 20 C. and the starch has largely 

 disappeared. 



Similarly, the cells of bulb-scales fully charged with soluble food- 

 materials (glucose, &c.) may exhibit no streaming until the sugar has been 

 largely removed. The decreased internal osmotic pressure will be accom- 

 panied by a rise in the percentage of water in the protoplasm, and by 

 a corresponding decrease in its viscosity. This, however, merely renders 

 streaming more easy, but does not cause it. The streaming may be 

 secondarily induced in correspondence with the fact that translocation from 

 a cell is accelerated by the existence of streaming movements in it. More- 

 over, when a cellular food- receptacle is being emptied, it usually passes 

 from a quiescent condition into a temporarily active one. When cells 

 which exhibit streaming are starved, the movement may not entirely cease 

 (Char a, Nitella) until shortly before death ensues, although in other cases 

 a long time may intervene between the cessation of streaming and the 

 permanent loss of vitality (Elodea^ Vallisnerid). If, when streaming has 

 become slow in chlorophyllous cells, they are exposed to light, a rapid 

 acceleration is usually exhibited, and the same commonly occurs when they 

 are supplied with dilute glycerine. The addition of dilute glycerine may, 

 however, accelerate streaming in well-nourished cells, and treatment with 

 strong glycerine followed by subsequent washing in water causes active 

 rotation to appear in previously quiescent leaf-cells of Elodea. Apparently 

 some obscure stimulating effect is exercised which may or may not be 

 connected with changes in the osmotic pressure, or in the percentage of 

 water present in the protoplasm. It has already been noticed that treat- 

 ment with dilute solutions of many neutral substances, including sugar, 

 potassium nitrate, and asparagin, may accelerate slow streaming, or induce 

 it when previously non-existent. Strong solutions of these substances, 



Cf. Ewart, Journ. Linn. Soc., 1896, Vol. XXXI, p. 565. 



