OTHER FORMS OF RADIANT ENERGY 71 



an hour to two hours, even in a few cases in which it ultimately permanently 

 ceases. 



Momentary exposure to darkness or bright light seems to have no 

 influence on streaming, but if preparations kept in darkness for some time 

 are suddenly exposed to concentrated sunlight, a temporary stoppage 

 lasting for a few seconds to a minute, or in Chara and Nitella a local 

 retardation, may often be seen. The latter is followed by a slight 

 acceleration, after which the streaming rapidly decreases and ultimately 

 ceases if the exposure is continued. 



If plants of Chara or Nitella are kept some days or weeks in darkness, 

 streaming becomes very slow, or moderately slow if the water is well 

 aerated. On exposure to bright diffuse light, streaming quickens within 

 five minutes, and may be four or five times as rapid within a quarter to half 

 an hour. Moore x concluded from similar observations on Chara vulgaris 

 that light acted as a direct stimulus accelerating streaming. If, however, 

 the plants are previously well aerated, streaming is more rapid to commence 

 with, and the acceleration is lessened and delayed by five or ten minutes. 

 If in addition the light is rendered as athermal as possible, a longer 

 exposure is necessary to produce any perceptible effect, and the ultimate 

 acceleration is still less pronounced. Obviously, therefore, the acceleration 

 is partly due to (i) a heating effect and (2) an increased percentage of 

 oxygen within the cell, for the chloroplastids of Chara can immediately 

 resume the assimilation of carbon dioxide even after the prolonged 

 absence of light. 



When the above precautions are taken, a noticeable acceleration on 

 exposure to light only occurs in specimens which have been in darkness 

 for two or three weeks, and are partially starved. In this case exposure 

 to light produces a renewed supply of food, and hence also of energy 

 for streaming. 



SECTION 29. Other Forms of Radiant Energy. 



Although streaming cells are very sensitive to electrical currents, they 

 seem to be insensible to electrical waves propagated through the ether. 

 At any rate streaming cells placed in various positions between two 

 syntonic Leyden jars, one of which was rapidly charged and discharged, 

 were unaffected, however well the second jar responded. It is, however, 

 possible that by a better arrangement positive results might be obtained. 



Atkinson 2 concluded that the Rontgen rays exercised no perceptible 

 influence on plants, but this was probably owing either to the exposure 



1 Journ. Linn. Soc., 1888, Vol. XXIV, p. 246. 



* Atkinson, Science Progress, 1898, Vol. vil, pp. 7-13; Lopriore, Nuova Rassegna, Catania, 

 1897; cf. also Bot. Ceutralbl., 1898, Bd. LXXIII, p. 451. 



