54 PHYSIOLOGY OF STREAMING MOVEMENTS 



the power is soon lost owing to the protoplasm of these strongly aerobic 

 fungi being soon fatally affected and the cells hence losing their turgidity 

 under such conditions. 



The death of the protoplasm causes the cessation of the changes in the 

 distribution of water and in the osmotic pressure to which the movements 

 are due. A direct dependence upon oxygen-respiration would certainly 

 have been inferred from these facts had not the precise causation of the 

 movement been known. Similarly, it is not impossible that many proto- 

 plasmic movements which are apparently vital in origin may not really be 

 so. For example, protoplasmic movement in Chara, Nitella, and in motile 

 anaerobic bacteria is largely or entirely independent of oxygen respiration, 

 and although we may assume that it is directly connected with respiratory 

 katabolism of some kind or other, the connexion might equally well be an 

 indirect or even accidental one. Dormant life without respiration is possible 

 in the case of many dry seeds and mosses, and similarly the power of move- 

 ment may be temporarily or even permanently inhibited without vitality 

 being impaired. 



'SECTION 21. Relation between Streaming and Assimilation. 



Streaming is always absent from very young cells in which assimilation 

 is active, and also from cells loaded with food- materials, although it may 

 appear as these are emptied. There is, however, no reason for assuming 

 a direct connexion between the two functions, and similarly with regard to 

 photosynthesis only indirect relationships appear to exist. In the absence 

 of free oxygen, however, streaming becomes dependent upon photosynthesis 

 in chlorophyllous aerobes. For example, if leaf-sections of Vallisneria or 

 leaves of Elodea are mounted in water, ringed with vaseline-paraffin mix- 

 ture, and kept in darkness, streaming usually soon ceases, but recommences 

 again on exposure to light. If the preparations are kept in darkness for 

 from eight to fourteen hours, streaming may not recommence on exposure 

 to light until after half an hour or more, and even after two hours may 

 be slow or barely perceptible 1 ; although similar preparations to which free 

 oxygen is admitted show active streaming in from thirty seconds to five 

 minutes. During this period of half to two hours the function of photo- 

 synthesis is temporarily in abeyance, but a facultative power of streaming 

 is usually present the whole time. If preparations are alternately illumi- 

 nated for five to ten minutes and darkened for a few hours, it will be found 

 that frequently streaming continues for a longer time in darkness than it 

 did after the second exposure, the cells evidently accommodating themselves 

 to a certain extent to the new conditions. 



If a closed cell-preparation of Elodea and Vallisneria is warmed to 



' x Similar observations have been made by F. Darwin. 



