PULSATING VACUOLES 295 



to Massart, Paramaecium aurelia forms numerous vacuoles when warmed 

 to 30 or 35 C. Similar vacuolations in the protoplasm of various plant- 

 cells were observed by Klemm * after the application of injurious agencies, 

 so that the phenomenon is probably a general one. 



In all cases the systolic contraction is very rapid, whereas the re-expan- 

 sion or diastole takes place much more slowly. The vacuole may reappear 

 at the same or another spot, and expands at first rapidly, but then more 

 slowly until it regains its original size, when it suddenly collapses again. 

 In the case of the plasmodia of Aethalium septicum and Chondrioderma the 

 maximal diameter of the contractile vacuoles varies from 0-004 to o-oi of 

 a millimetre 2 , but when the vacuoles are large the systole, though rapid, can 

 be followed, and often does not lead to the entire disappearance of the 

 vacuole. 



The pulsatile frequency varies according to the external conditions, 

 and attains a maximum at a somewhat variable optimal temperature. 

 Under favourable circumstances 12 to 15 seconds may elapse from one 

 systole to the next in the case of the zoospores of Vlothrix 3 , and 26 to 60 

 seconds in the case of Gonium 4 . The duration of each period, is however, 

 usually 60 to 90 seconds 5 in the case of the plasmodia of Aethalium and 

 Chondrioderma, and the vacuoles of these organisms which do not com- 

 pletely empty often pulsate still more slowly 6 . In the case of the 

 Infusorian Spirostomum teres the pulsatile frequency is given as 30 to 40 

 minutes 7 , so that vacuoles may exist in plants which pulsate so slowly 

 that hitherto their special character has not been detected. 



Although the pulsation usually maintains the same frequency under 

 constant external conditions there are naturally exceptions to this rule. 

 Cienkowski 8 observed a very variable frequency in certain Palmellaceae, 

 and the same applies to those vacuoles of plasmodia which undergo 

 imperfect systole 9 . In addition neighbouring vacuoles of plasmodia may 

 be in all stages of systole and diastole at the same moment, whereas when 

 two vacuoles only are present one is usually expanding while the other 

 collapses 10 . In many cases, as for instance in certain Palmellaceae, both 

 vacuoles contract at the same time. 



1 Klemm, Desorganisations-Erscheinungen in pflanzlichen Zellen, Jahrb. f. wiss. Bot., Bd. 

 xxvin, 1895, P- 68 5- 



Pfeffer, 1. c., p. 192. 3 Strasburger, 1. c. ; Dodel, 1. c. 



Cohn, Nova Acta Acad. Caesar. Leopold., 1854, Bd. xxiv, i, p. 196; Biitschli, Protozoen, 

 1880-8, pp. 714, 1453, gives summaries of the pulsatile frequency in various Infusoria. 



Cienkowski, Jahrb. f. wiss. Bot., 1863, Bd. in, p. 329. 



Pfeffer, Zur Kenntniss d. Plasmahaut u. d. Vacuolen, 1890, p. 192. 



Biitschli, I.e., p. 1454. 8 Cienkowski, Bot. Ztg., 1865, p. 22. 



In the individual cells of colonies of Gonium approximately the same rhythm may sometimes 

 be maintained. 



10 SeeButschli, I.e., p. 713. 



