PRECIPITATION STRUCTURES SIMULATING ORGANIC GROWTH. 257 



regular rhythmic motion which lasts for several minutes. A thin 

 and almost transparent membrane swells up rather quickly and 

 then a. small saccule shoots out at the side; at this instant the 

 membrane falls back, seemingly the pressure against it being 

 relieved. This process continues for several minutes in each 

 case and finally slows down and stops. The thin membrane 

 never seems to rupture except at its edge where the little sac- 

 like structures are formed. In some cases small filaments form 

 also and radiate out around the membrane. 



After several hours many such groups have formed and the 

 whole presents a striking appearance. This phenomenon is 

 not frequent with iron filaments, although some cases have been 

 observed (Fig. 6). In these the vesicles are usually smaller, 

 they form more quickly and a larger proportion of fine filaments 

 are formed. Such structures are frequently formed from cobalt 

 filaments and in this case are always much larger than those 

 formed from iron or zinc (Figs. 16, 17). They vary from 200 

 to 300 microns in diameter, the enclosing membranes are thicker, 

 and the whole structure is somewhat oblong in shape. The 

 exact manner of formation has not been observed; no rhythmic 

 motion has been seen. 



6. Influence of Mechanical Contact. Contact with solid ob- 

 jects has a marked influence on both the direction and rate 

 of growth. In some cases filaments have shown tendril-like 

 tendencies. Cases were observed in which Fe-ferricyanide 

 filaments have wound spirally around a fine iron wire as often 

 as nine times. Filaments of all the metals used show some reac- 

 tion to contact with other bodies. Fig. 9 shows three filaments 

 following along side by side for some distance. 



7. The retarding and accelerating effects on the growth of 

 precipitation structures observed in combinations of metals of 

 different solution-tension have already been "studied and de- 

 scribed in full by R. Lillie. 1 



V. Rhythmical Phenomena in Growing Filaments and Other 

 Structures. Rhythmic motion is not evident in the formation 

 of filaments in all cases, as, e. g., in the filaments formed from 

 iron. These seem to grow by an even and regular deposit of 



1 Lillie, loc. ell., pp. 144-146. 



