CHANGES OF CONCENTRATION AND OF TURGIDITY 57 



sionally be seen in non-nucleated fragments which have no protoplasmic 

 connexions with the nucleus, or which may even be cut off from it by 

 ingrowths of cellulose l . 



Another mode of experimentation is to replace fragmented cells 

 with plasmolyzed protoplasts in more dilute solutions, or ultimately 

 water, after the nucleated portions have become covered with a new 

 cell-wall. The expansion is naturally more marked in the non-nucleated 

 portion than in that covered by a cell-wall, even when the latter is still 

 thin. The rapidity of streaming usually increases, but it ceases more 

 rapidly in the non-nucleated portion than normally. As the percentage of 

 water in the protoplasm increases, its respiratory activity will increase, 

 while its viscosity decreases. Hence the increased velocity. When the 

 restraining influence of the nucleus is removed, either katabolism seems to 

 preponderate over anabolism, or assimilation decreases, so that the non- 

 nucleated cytoplasm wastes away even under optimal nutritive conditions. 

 Hence, in water or dilute sugar solution the increased respiration causes 

 a more rapid consumption of the available plastic material, so that although 

 the velocity of streaming is temporarily enhanced, the duration of the 

 movement is lessened. 



SECTION 24. Changes of Concentration and of Turgidity. 



The effect of these has already been discussed from a purely physical 

 point of view, but in addition a physiological stimulating action may be 

 exercised. Thus the shock of immersal in dilute saline solutions suffices to 

 cause a temporary stoppage of streaming lasting from one to ten minutes, 

 which is very different in its origin from the gradual slowing and ultimate 

 cessation of streaming which may be produced by the chemical action of 

 the dissolved substance. These facts were first observed by Dutrochet in 

 Chara, and Hermann finds that a similar shock-stoppage may readily be 

 produced in Nitella 2 . A shock-stoppage may also be produced in Elodea, 

 Vallisneria, and Trianea by suddenly applying nearly isosmotic saline 

 solutions, but this result is naturally more difficult to attain in cuticularized 

 hair-cells (Tradescantia, Urtica, Cucurbita). After the cells have accus- 

 tomed themselves to the concentrated solution, a shock-stoppage may again 

 be produced by suddenly immersing them in water (cf. Dutrochet, 1. c.). 



Hermann found that if one half of a cell of Nitella was immersed in 

 water, and the other in 5 per cent, sugar solution, streaming soon recom- 

 menced in both halves, but was slower in the end in sugar solution than in 

 that in water. He regards this as the result of the tonic stimulating action 



1 Cf. Ewart, Trans. Liverpool Biol. Soc., 1895, Vol. ix, p. 199. 



a Dutrochet, Ann. sci. nat., 1838, p. 71 ; Hermann, Studien viber Protoplasmastromung der 

 Characeen, Jena, 1898, p. 51. 



