CHEMOTAXIS AND OSMOTAXIS 345 



ing powers than malic acid. Potassium nitrate and ammonium phosphate 

 exert a still feebler attractive action, which is easily overlooked, but Buller 

 was unable to detect any chemotactic response to sodium chloride, ammonium 

 nitrate, calcium chloride, sugars, asparagus, and glycerine l . 



Inactive malic acid acts similarly to the active form, while the free 

 acid and its neutral salts seem to have the same excitatory value 2 . On 

 the other hand, the diethylester of malic acid, in which the acid is not 

 present as an ion, exercises no chemotactic action 3 . Malic acid exerts a 

 repelling action when concentrated, but not its salts, and Buller 4 (I.e., p. 560) 

 has shown that the chief attractive substance in the archegonium may be 

 a salt of malic acid, possibly potassium malate, but cannot be free malic 

 acid. Since the repulsion may be produced by citric and other acids, 

 we have probably before us a reaction dependent upon the mere increase of 

 acidity, i. e. upon the relative number of hydrogen ions 5 . Strong alkaline 

 solutions, and sufficiently concentrated solutions in general, exercise a certain 

 repulsion, which is often only shown at first, and which does not prevent the 

 gradual entry of large numbers of the antherozoids into the capillary 

 tubes, in which they soon become motipnless and die 6 . They have, there- 

 fore, not the power of avoiding all injurious liquids, and are readily attracted 

 to their death by introducing a tube containing malic acid mixed with 

 a little mercuric chloride 7 . The chemotaxis of these antherozoids is the 

 result of a typical tactic reaction 8 , and the same appears to apply to the 

 negative chemotaxis produced by free acids. It is, however, not yet certain 

 whether the osmotactic repulsion produced by concentrated solutions is 

 a tactic or a phobic reaction. 



SPECIAL CASES. A salt of malic acid is probably also the chief 

 attractive stimulus for the sperms of Selaginella, and possibly cane-sugar 

 for those of Mosses, since the latter suffices to produce a perceptible 

 attraction when diluted down to o-ooi per cent, strength 9 . The sperms of 

 Hepaticae, of Sphagnum, and of Marsilia seem to be attracted into the 

 archegonium in the same way, but the attractive substances have yet to be 

 found 10 . 



Cf. Buller, Annals of Botany, 1900, Vol. xiv, pp. 548, 571. 

 Pfeffer, 1. c., Vol. II, pp. 381, 654; Voegler, 1. c., p. 659. 

 Pfeffer, 1. c., p. 371. * Buller, 1. c., p. 560. 



Pfeffer, 1. c., p. 387; Buller, 1. c., p. 567. 



Pfeffer, 1. c., p. 385. Buller (1. c., p. 555) observed only weak repulsion or none at all, and 

 was unable to detect the transitory repulsion. Much depends upon the manner in which the experi- 

 ment is performed. 



7 Pfeffer, 1. c., p, 388. 8 Cf, Rothert, Flora, 1901, p. 388. 



9 Pfeffer, 1. c. 1884, pp. 422, 430. Other substances may also exert a slight action. 

 10 Pfeffer, 1. c., 1884, Bd. I, pp. 434, 435; 1888, Bd. II, p. 655. On the process of fertilization 

 in Hepaticae cf. Strasburger, Jahrb. f. wiss. Bot., 1869-70, Bd. vn, p. 402; Leitgeb, Flora, 1885, 

 P- 330. 



