SEPARATE LOCALIZATION OF PERCEPTION AND RESPONSE 201 



transference, but how this is produced is quite uncertain. We may, 

 however, conclude with reasonable certainty that the protoplasmic com- 

 munications play an important or even essential part in the conduction 

 of stimuli. The fact that stem and roots are incapable of any geotropic 

 reactions when plasmolysed does not afford conclusive proof 1 , since the 

 treatment probably acts by suppressing the growth reaction. The fact 

 that the influence of the external conditions upon the rapidity and readiness 

 of transmission of stimuli corresponds to their influence upon perception 

 and' sensation indicates that the former also is a vital phenomenon ' 2 . The 

 possibility of the transverse conduction of stimuli is probably owing to 

 the presence of interprotoplasmic communications on the side walls, their 

 distribution being such as to restrict the stimuli to particular paths 3 . 

 There appears, however, to be a certain ^time block at each passage 

 from cell to cell, and it is for this reason that longitudinal propagation 

 is always more rapid in tissues composed of elongated cells than trans- 

 verse propagation. The times usually given for the transference t of 

 stimuli include the latent period of response, but by eliminating this 

 Ewart found that traumatic stimuli inducing streaming travelled at rates 

 of i mm. to 2 mm. per minute at 30 C. 4 Within the long cells of Chara 

 and Nitella,2(. much more rapid prolongation of stimuli inhibiting streaming 

 is shown when the time of reaction is excluded, for they travel at a rate 

 of i mm. to 8 mm. per second at room temperatures "'. 



The protoplasmic fibrillae which NSmec 6 considered to be the channels for the 

 transmission of tropic stimuli may favour the transmission in a special direction. 

 According to Nemec, they become more strongly marked as the result of stimulation, 

 and, if so, this may explain why a continuous stimulation may spread further than 

 a single excitation. The fibrillae do not, however, form a continuous conducting 

 system, nor are they always present 7 , while in the latter case stimuli may be trans- 

 mitted as rapidly, or even more rapidly, than when they are present 8 . Czapek 9 

 found that reducing substances increased in amount in geotropically-excited root- 



1 Strasburger, Jahrb. f. wiss. Bot., 1901, Bd. XXXVI, p. 578. 

 * Czapek, ibid., 1898, Bd. xxxn, p. 221. 



3 Cf. Stiasburger, I.e., 1901, Bd. xxxvi, p. 493; Kienitz-Gerloff, Ber. d. hot. Ges., 1902, 

 P-93- 



' Ewart, The Physics and Physiology of Protoplasmic Streaming in Plants, 1903, p. 105. 



5 Ewart, 1. c., p. 103. 



6 N6mec, Die Reizleitung und die reizleitenden Structnren, 1901, p. 135 ; Biol. Centralbl., 1901, 

 Bd. xxxi, p. 529. 



7 Haberlandt, Sinnesorgane im Pflanzenreich, 1901, p. 150; Biol. Centralbl., 1901, Bd. XXXI, 

 [>. 369 ; Ber. d. bot. Ges., 1901, p. 569. On the conduction of stimuli in nerves cf. Verworn, Das 

 Neuron in Anatomic und Physiologic, 1900. See also the summary by Boruttau, Zeitschr. f. allgem. 

 Physiol. von Verworn, 1901, Bd. I, p. 129. 



8 Ewart, 1. c., 1903, p. 102. 



9 Czapek, 1. c., p. 208 u. Ber. d. bot. Ges., 1901, Generalvers., p. 122. 



