370 Mr. J. Clark. Protoplasmic Movements and [June 20, 



XVI. " Protoplasmic Movements and their Relation to Oxygen 

 Pressure." By James Clark. Communicated by Professor 

 Vines, F.R.S. Received June 19, 1889. 



(Abstract.) 



That the presence of free oxygen is one of the essential conditions 

 of protoplasmic movements has long been recognised. Further than 

 this however the subject has not hitherto been investigated. 



The following are the results of a long series of experiments made 

 to ascertain the minimum pressure of oxygen necessary to restore the 

 streaming, amoeboid and ciliary movements of protoplasm after they 

 have come to rest in the absence of that gas. The object experi- 

 mented upon was in each case placed in a hanging drop of water and 

 exposed to an indifferent gas such as hydrogen or nitrogen, or else 

 put into connexion with the exhausted receiver of an air-pump. In 

 the former case when the observed movement had ceased a current of 

 indifferent gas containing a definite percentage of oxygen was passed 

 over the object ; in the latter a small quantity of air was admitted 

 and the pressure registered. By varying in successive experiments 

 the percentage of oxygen mixed with the diluent gas, and the quantity 

 of air admitted into the air-pump, the minimum pressure of oxygen 

 necessary to restore movement could be ascertained by both methods, 

 so that one could act as a check upon the other. 



In this way the minimum for the streaming movement in the 

 plasmodia of Myxomycetes, and in the cells of hairs, of parenchyma, 

 of xylem, phloem and cambium was found to vary from 1 mm. to 

 over 3 mm. It was lowest for the plasmodia of Myxomycetes, the 

 minimum for Chondrio derma difforme being 1 mm., and for Didymium 

 farinaceum 12 mm. Except with very old plasmodia the results 

 obtained even with unfavourable specimens rarely exceeded 2 mm. 

 With the vegetable cell the variation was much more extensive. In 

 such a favourable object as the root hairs of Trianea bogotensis a 

 minimum of 1*2 mm. was occasionally obtained, whereas for the 

 partly cuticularised leaf hairs of Urtica americana it sometimes 

 exceeded 3 mm. With the cells of the parenchyma the experimental 

 difficulties were usually very great, and for those of the xylem, phloem, 

 and cambium still more so. With the former the minimum found 

 for each plant usually lay between 2 mm. and 3 mm., and was some- 

 times even less. With the latter, cells of all three were found which 

 gave similar results but these were rare, as death of the cell contents 

 usually arrested the experiment. It seems probable however that if 

 variation due to experimental difficulties and the resistance of the 

 cell wall to the passage of oxygen could be eliminated, the minima 



