100 



MOLAR AGENTS AND PROTOPLASM 



[CH. IV 



upon shaking. When alga cells, such as those of Chara or 

 Vallisneria, are freshly transferred to the slide, the disturbance 

 causes cessation of movements (HOFMEISTER, '67, p. 50). 

 When the stamen hairs of Tradescantia are crushed, the stream- 

 ing of the plasma ceases. When Chara is cut across or punct- 

 ured, rotation stops for a longer or shorter time (DUTROCHET, 

 '37, p. 780). Even when a stem of Chara is pricked at the 

 node by a needle, without penetrating into the cavity, move- 

 ment ceases for a minute 

 or two. Thus, mechanical 

 disturbance profoundly af- 

 fects protoplasm. 



Let us now consider 

 more in detail the changes 

 which take place in the 

 protoplasm. VERWORN 

 ('92, p. 24) has given 

 us data on this matter. 

 Orbitolites is a rhizopod 

 having extremely deli- 

 cate, filamentous pseudo- 

 podia. If one of these 

 pseudopodia be cut across 



as at z, Fig. 13, 



the 



FIG. 13. Pseudopodium of Orbitolites, re- 

 tracting as a result of local stimulation. 

 The arrows give the direction of the 

 streaming of protoplasm. At the left is 

 shown the beginning of the excitation ; at 

 the right, its end. (From VERWORN, '92). 



following changes occur : 

 the protoplasm lying next 

 the cut directly collects 

 into small spherical or 

 fusiform masses which be- 

 gin to migrate centripe- 

 tally (Fig. 13, 6). This movement meets with the normal 

 centrifugally migrating plasm and turns the latter towards the 

 centre again (Fig. 13, c). Gradually the thickenings elongate 

 until, before they have reached the central body, they are no 

 longer visible (Fig. 13, cT). In about 2 minutes normal move- 

 ments are completely restored (Fig. 13, e). Slightly different 

 results are gained from Cyphoderia (Fig. 14). When the 

 large pseudopodium of this organism is touched with a needle 

 near its distal end, it thickens (as in the case of Obitolites) and 



