ELEMENTARY VITAL PHENOMENA 



225 



c. Movements by Change of the GcU-tiorgor 



With movements caused by a change of the cell-turgor, we 

 begin the consideration of those phenomena of motion that pre- 

 suppose normal life in the object in which they appear. 

 With the death of their substratum they are extinguished. 

 Turgescence-movements are chiefly found among plants ; and it is 

 necessary, therefore, that certain peculiarities of the plant-cell be 

 recalled. 



The plant-cell, as is well known, is a cylindrical capsule, the 

 alls of which are formed by an elastic membrane of cellulose. 



B 



s 



Fig. 90. — Scheme of cell-turgor of a plant-cell ; /i, cell-membrane ; p, primordial utricle ; k, nucleus ; 

 r, chlorophyll-bodies ; s, cell-sap ; c, infiltrating salt solution. In A^ the cell is in complete tur- 

 gescence, the primordial utricle lies close to the cell-membrane. In S the tiirgor has decreased 

 as a result of the action of a salt solution, the cell has become smaller, but the primordial utricle 

 still lies in contact with the cell-membrane. In C the turgor has become still less, the pri- 

 mordial utricle is beginning to be puUed away from the cell-membrane, which latter has 

 reached its minimum. In D the primordial utricle has contracted completely, because the 

 osmotic effect of the salt solution acting from the outside has reached a very high degree. 

 (After de Vries.) 



The inner surface of the capsule is covered by a thin but con- 

 tinuous protoplasmic layer, the so-called primordial utricle, 

 which encloses like a sac or bladder a liquid, the cell-sap, and as 

 a rule sends through the large vacuole strands of protoplasm 

 which branch lengthwise and crosswise (Fig. 90 ; in this figure 

 the strands are wanting). Various chemical substances, which 

 have been produced by the vital activity of the cell, are dissolved 

 in the sap. In its usual uninjured condition the protoplasm is 

 impermeable to these substances, hence they cannot diffuse from 

 the interior to the outside through the primordial utricle. But 

 the protoplasm is likewise impermeable to many substances that 

 are dissolved in the water outside the cell, and which, therefore, 



