332 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



The orientation cannot be determined by the assimilatory activity, since it is 

 produced almost solely by the more refrangible rays, and hardly at all, or not at 

 all, by the less refrangible ones which are most active in photosynthesis *. Accord- 

 ing to Frank, light which has passed through a solution of potassium bichromate 

 exercises a feeble action, but Borodin and Schmidt could detect no action at all, 

 possibly owing to the use of more concentrated solutions or thicker screens. Chromo- 

 plasts, leucoplasts 2 , and etiolated chloroplastids * show no power of phototactic 

 orientation, but it must be remembered that we are dealing with a special irritability 

 which is not developed by all chloroplastids. Chromoplastids may, however, occur 

 in plants which are capable of phototactic responses, such as are shown by certain 

 non-chlorophyllous zoospores, and by the pigment cells of such animals as the 

 chameleon 4 . According to Berthold 5 , peculiar plasmatic plates occur in Chylocladia 

 which are capable of phototactic reaction like chloroplastids. No evidence as to the 

 mode of orientation is, however, afforded by the fact that it ceases in the absence of 

 oxygen 6 , or as the result of etherization 7 , and is also more or less influenced by the 

 external conditions in general. 



An unequal distribution of the chloroplastids may either be produced purely 

 mechanically as the result of the shape of the cell, or by gravitational or surface-ten- 

 sion forces, or it may be due to the physiological polarity of the protoplasm, or to the 

 action of the external conditions. In darkness the chloroplastids in the leaf-cells of 

 a Moss collect upon the walls at right angles to the surface, while those in the interior 

 of tissues have a tendency to avoid the surfaces and to collect on the walls border- 

 ing the intercellular spaces where air is present 8 . The utility of this arrangement 

 is obvious, but according to Haberlandt the chloroplastids have a general tendency 

 to avoid those walls through which continuous translocation occurs. Frequently 

 the chloroplastids leave the peripheral protoplasm and they often tend to collect around 

 the nucleus, so long as they contain no large starch-grains *. 



Rapidity of the reaction. This is especially pronounced in the chlorophyll-bands 

 of Mesocarpus 10 , but the chloroplastids of Funaria and other plants may pass in less 



1 Borodin, Ueber die Wirkung d. Lichts auf die Vertheilung der Chlorophyllkorner, 1869, p. 58 

 (Melanges biologiques, Bd. vu) ; P. Schmidt, Ueber einige Wirkungen des Lichts auf Pflanzen, 1870, 

 p. 27; Frank, Bot. Ztg., 1871, p. 228. 



3 Schimper, 1. c., p. 204. 



3 According to observations by Senn. 



4 O. Hertwig, Die Zelle u. d. Gewebe, 1893, p. 8r. 



5 Berthold, Jahrb. f. wiss. Bot., 1882, Bd. xin, p. 690. 



6 Demoor, L'etude de la physiol. de la cellule, 1894, p. 54 (reprint from the Archives de 

 Biologic, Bd. XTII). Lewis (Annals of Botany, 1898, Vol. XII, p. 421) observed a phototactic reaction 

 of the chlorophyll plate of Mesocarpus in an atmosphere of hydrogen, but in this case oxygen is pro- 

 vided by the assimilation of the carbon dioxide produced within the cell. 



7 Elfving, Ueber die Einwirkung von Aether u. Chloroform auf d. Pflanze, 1886, p. 16 (reprint 

 from the Ofversigt af Finska Vetensk. Soc. Forh., Bd. xxvin). 



8 Stahl, Bot. Ztg., 1880, p. 332 ; Haberlandt, Ber. d. bot. Ges., 1886, p. 217. 



9 Schimper, 1. c., p. 206; Berthold, Protoplasmamechanik, 1886, pp. 140, 169; Haberlandt, 

 Flora, 1888, p. 304. 



10 See Stahl, 1. c., p. 301 ; Oltmanns, 1. c. ; Lewis, 1. c., p. 418. Lewis investigated the induction- 

 period and after-effect. 



