THE INFLUENCE OF ILLUMINATION 319 



Further instances of such actions may ultimately be discovered, and much 

 depends upon the condition of tone of the organism, which largely depends 

 upon external circumstances. 



According to Josing T , the action of ether or the withdrawal of carbon 

 dioxide causes streaming to cease in darkness and to recommence on 

 illumination, whereas under normal conditions it is about as rapid in dark- 

 ness as in light. Thus Josing states that in leaf- eel Is of Vallisneria spiralis 

 in water containing from 0-25 to i per cent, of ether, streaming ceases after 

 darkening for ten minutes to half an hour, and recommences thirty seconds 

 to five minutes after reilluminating. Chloroform acts in the same way, 

 but not alkaloids or alcohol 2 . Similar, but slower, reactions are shown 

 when hanging-drop preparations are made in a gas-chamber, the floor of 

 which is covered by caustic soda. If, however, a non- volatile acid is added 

 (i of phosphoric acid or of citric acid in 10,000, and 20,000 of water 

 respectively), the streaming persists in darkness as well as in light. Since 

 non-chlorophyllous objects react in the same way, the recommencement of 

 streaming on exposure to light cannot be due to the photo-synthetic 

 production of oxygen. 



[It is doubtful whether the action of ether actually depends upon the condition 

 of phototonus. Very dilute solutions of ether may slightly accelerate streaming, but 

 solutions of the strength given retard it 8 . The rise of temperature produced in 

 a strongly illuminated gas-chamber will cause ether to pass into the air of the chamber, 

 and the hanging drop to contain less ether, whether the floor of the chamber is covered 

 with a similar solution of ether or not and whether the chamber is open or closed. In 

 this way the retarding action exercised in darkness would be lessened on illumination, and 

 might even be converted into an acceleration. Josing states, however, that it is the blue 

 rays, and not the red ones, which excite streaming in the etherized preparations. In any 

 case I am quite unable to confirm the statements of Josing in regard to the effects of 

 the withdrawal of carbon dioxide, streaming continuing on the average equally long in 

 similar preparations of Vallisneria kept in darkness, whether small amounts of carbon 

 dioxide were present or not, sometimes the one and sometimes the other coming to rest 

 first. Further, cells of Vallisneria frequently continued to show streaming for more 

 than a day in darkness, although the carbon dioxide was continually removed and no 

 external acidity was present. Any considerable accumulation of carbon dioxide 

 retards streaming both in light and darkness, and cells of Chara and Nitella continued 

 to show slow streaming, although the carbon dioxide was continually withdrawn and 

 the plants kept in darkness for as long as six weeks*. Finally, the o-oi per cent, 

 solution of phosphoric acid which, according to Josing, causes streaming to continue 

 in darkness, produces a stoppage of streaming in Chara and Nitella within an hour or 

 two, and in Elodea and Vallisneria within a day 5 .] 



1 Josing, Jahrb. f. wiss. Bot., 1901, Bd. xxxvi, pp. 198, 210. 2 Josing, 1. c., p. 214. 



8 See Ewart, Protoplasmic Streaming in Plants, 1903, p. 86. 



4 Ewart, 1. c., p. 42. 8 Cf. Ewart, 1. c., p. 77. 



