THE TRANSLOCATION OF PROTOPLASM 83 



wound heals and streaming may be resumed. Light, when alter- 

 nated with darkness, may cause or accelerate streaming. Streaming 

 may be caused by a sudden change of temperature of several degrees. 

 Streaming may occur or be caused to take place in unbranched as 

 well as in branched filaments. 



Arthur and, subsequently, Schroter had stated that in Rhizopus 

 nigricans, when streaming is actively taking place in the centre of 

 a hypha in one direction, a thin peripheral sheath -like non-vacuo- 

 lated layer of protoplasm can sometimes be seen moving in the 

 opposite direction, and both these authors had indicated the double 

 current in a text-figure (for Arthur's illustration vide Fig. 46, B). 

 However, Andrews was not only unable to observe any peripheral 

 return current in a streaming hypha but positively denied its 

 existence : " There is no streaming or movement in the opposite 

 direction as stated and figured by Schroter ... I can therefore 

 not agree with Schroter on this point but find, as stated by Ternetz 

 for Ascophanus carneus, that during streaming all of the moving 

 protoplasm of Mucor stolonifer and M . Mucedo goes only in one 

 direction. It is hardly possible, even if a reverse movement did 

 take place along the wall during streaming, that it would be sufficient 

 to account for the return of the protoplasm. The streaming occurs 

 first in one direction, and when the factor that has caused this 

 subsides or is overcome, it streams back in the opposite direction." 



In 1932, assisted by one of my pupils, Mr. C. C. Neufeld, I 

 examined cultures of the mycelium of Rhizopus nigricans with a 

 view to finding out whether or not the return current in streaming 

 hyphae can be observed. Spores were sown in hanging drops of 

 5 per cent, cane-sugar solution. Forty-one hours later the mycelia 

 were found to be well developed. The temperature of the room 

 was about 26° C. After the cover-glasses had been raised for a 

 short time, streaming became very active in the thicker hyphae. 

 In a number of these hyphae the double flow of protoplasm in opposite 

 directions was clearly seen — a rapid massive streaming of protoplasm 

 and vacuoles down the centre of a hypha in one direction, and a 

 peripheral flow of a very thin sheath-like layer of non-vacuolated 

 protoplasm in the opposite direction. The particles in the peri- 

 pheral stream of protoplasm were watched moving quite steadily 



