PROTOPLASM MOVEMENTS. 9 



While in thinner protoplasm the streaming and mass- 

 movements are always horizontal, or, at least, parallel with 

 the surface upon which tht; plasmodium rests, in the case of 

 tougher protoplasm they may give rise to branches which 

 have an upward direction, as in the formation of sporangia. 



9.— Effect of External Influ3nces. The movements of 

 .the protoplasm of the Myxomycetes, and probably to a 

 greater or less extent of all plants, are suspended by certain 

 external influences. Violent jarring, pressure, a thrust as 

 with the point of a pin or pencil, electrical discharges, 

 sudden changes of the temperature, and sudden changes in 

 the concentration of the surrounding fluid, stop the move- 

 ments, and cause the plasmodium to contract into one or 

 more spheroidal masses. "When these influences cease, if 

 they have not been so violent- as to destroy the organization 

 of the protoplasm, it returns after a greater or less length 

 of time to its original form, and the movements are resumed. 



(fl) The effdct of mechanical disturbances (jarring, pressure, and 

 thrust) may be best studied in tlxe tougher or least fluid plasniodia 

 (e.g., of Stemonitis fusca). 



(6) The effect of electrical discharges may be studied by placing a 

 small Plasmodium {e.g., Didymium serpula) upon a glass plate provided 

 with platinum points which are in connection with the poles of an 

 induction apparatus. When a discharge takes place through a narrow 

 branch (pseudopodium) it contracts so violently as to be broken up into 

 a row of little spheres ; if it takes place through the mass of the Plas- 

 modium it becomes more or less spherical by its contraction. In any 

 case, if the shock has not been too severe, the protoplasm after a while 

 returns to its normal shape again.* 



(c) The Plasmodium of Didymiwm serpula, when removed from a tem- 



* KuUne performed the following curious experiment. Taking a 

 portion of the plasmodium of Didymium serpula, in its resting state, 

 lie mixed it with water so as to make a pulpy or pasty mass. With 

 thi§ he filled a piece of the intestine of a water-beetle, and tying the 

 ends, laid it across the electrodes of an induction apparatus. The pre- 

 paration was kept in a film of water in a damp chamber for twenty-four 

 hours, at the end of which time it was considerably distended. He now 

 allowed the electrical current to pass throuirh it, when it contracted 

 itself "like a colossal muscle-fibre.'' Upon extending it by pulling at 

 the ends, and then sending through it a stronger electrical current, it 

 contracted itself i.ne third of its length. 



