PASSIVE OR ACTIVE MOVEMENTS BY CHLOROPLASTIDS 107 



chloroplastid with a power of spontaneous movement. All these con- 

 clusions of Hermann's are, however, practically based upon the single 

 above-mentioned observation made upon a dying cell of Nitella, an 

 observation, moreover, which the writer has been unable to repeat. 

 Against it we have the following positive observations: (i) rotating chloro- 

 plastids exert no such counteraction upon neighbouring particles as might 

 be expected if they possessed an active power of movement differing from 

 that in the cytoplasm ; (2) chloroplastids killed and bleached by sunlight 

 may exhibit the same rotary movements as living ones, and it is highly 

 improbable that a dead chloroplastid could maintain permanently attached 

 to it the active layer of protoplasm that Hormann postulates ; (3) isolated 

 chloroplastids never show any active translocatory movements, however 

 long they may remain living under observation 1 . 



Velten (1. c.) observed that when the protoplasm was coming to rest, 

 the chloroplastids often appeared to strike against the plasma, and con- 

 cluded from this that all chloroplastids possess an active power of trans- 

 locatory movement. Dutrochet (1. c., pp. 17, 73) even went so far as to 

 regard the chloroplastids as the active agents in producing streaming 

 movements in Chara and Nitella. Obviously Dutrochet was unaware of 

 the existence of streaming in the non-chlorophyllous rhizoids of these plants. 

 Velten's conclusion is decisively negatived by the fact that dead bleached 

 chloroplastids may exhibit the same phenomenon as that observed by him. 

 The peculiarity is probably due to one or more of the following factors : 

 (i) the momentum of the chloroplastids, (2) local variations in the viscosity 

 of the protoplasm, and hence unequally distributed internal friction, (3) 

 local inequalities in the activity of the propulsive mechanism. 



A closely allied question is whether the slow epistrophic and apostro- 

 phic movements of the chloroplastids due to the action of light are active 

 or passive in character. In some cases, as for example in Mesocarpus, it 

 has been tacitly assumed that the movement was active, although no direct 

 proof has ever been brought forward. It is certainly suggestive that in 

 motile unicellular organisms, the movements carried out under the action 

 of light are performed by the entire organism, and not by the chlorophyllous 

 part of it. Similarly in higher plants, it is the protoplasts as a whole which 

 perceive and respond to light-stimuli. It is even doubtful whether the 

 chloroplasts act as percipient organs for light at all. 



According to Frank 2 , however, the movements are passive, whereas 

 Moore 3 considers them to be active. The latter author is, however, unable 

 to adduce sufficiently satisfactory evidence in support of his view. Isolated 



1 Cf. Ewart, Journ. Linn. Soc., 1896, Vol. xxxi, pp. 423-7. 



2 Bot. Ztg., 1872 ; Jahrb. f. wiss. Bot., 1872, Bd. vni. 



3 Journ. Linn. Soc., 1888, Vol. XXIV, p. 240. 



