258 



The Structure of Protoplasm 



a mechanism is applicable to a myxomycete plasmodium, for the 

 following several reasons. 



A Plasmodium is an aggregate of many regions, each of which is 

 a unit in itself. Each contains liquid, flowing protoplasm surrounded 

 by firm and quiet protoplasm, and each possesses its own rhythm. 

 Three rhythms were shown in my original moving pictures of Plas- 

 modia, and no two of the three were pulsating in unison. Were the 

 mechanism of flow situated in a single protoplasmic part, the peri- 

 pheral layer, it is hardly likely that there would be a duphcity of 

 rhythms. One may frequently observe in a plasmodium several 



lines of flow which cannot 



-e- 



->- 



/\ 



/V 



possibly be the expression of 

 a single contractile mechan- 

 ism. Illustrations of two such 

 situations are shown in Fig- 

 ures 4 and 5. Figure 4 is a 

 diagram of two connecting 

 strands with arrows which 

 indicate six possible types of 

 flow all seen within a few 

 Such a situation can be adequately accounted for 

 of several frequencies not in perfect 



Fig. 4. Six possible combinations in 

 direction of flow in two connecting strands. 



minutes' time 



only on the assumption 



synchronism. There is a lag in the time of reversal in one strand 



over that in the other, which means that there is more than one 



center of contraction in the plasmodium. 



Figure 5 illustrates another case where contraction is not cen- 

 tered in the surface layer, but at a point, or points, some distance 

 in from the surface. 



The six possible types of flow shown in Figure 4 are reproduced 

 many times over by numerous small individual systems or centers 

 of activity throughout a plasmodium. In short, there is not one 

 surface layer of contractile protoplasm, but many secondary centers 

 of contractility. 



A situation that one would have difficulty in interpreting on the 

 basis of a single contractile mechanism is that involving the flow of 

 protoplasm in a globule. Were a spherical plasmodium a shell of 

 firm contractile protoplasm enclosing a core of fluid non-contractile 

 protoplasm, then uniform contraction of the surface would compress 

 the inner protoplasm and not produce flow along defined channels; 

 but if this droplet of protoplasm consists of many individual centers 



