THE CONDUCTING CHANNELS 217 



whether the presence of well- developed bordered pits in the wood of 

 Coniferae is intended more for mechanical support than for purposes of 

 exchange, or whether these pits subserve quite different functions 1 . 



It is one of the aims of physiological science to determine the 

 functional importance of these and other arrangements, but any attempt 

 to directly deduce the functional importance of an organ from its visible 

 structure frequently leads to one-sided or erroneous conclusions. For 

 example, Godlewski (Sect. 36) has attempted to use the anatomical 

 arrangement of the wood elements as an argument in support of his 

 vitalistic theory of the ascent of water, whereas Strasburger with equal 

 force contends that the arrangement indicates the absence of any such 

 vital action. Moreover it must be remembered that the structural ar- 

 rangement is such as to permit of the transference of water in both 

 directions. 



The lateral connexions in the vascular bundles also allow water to 

 pass along oblique paths, as has been shown by various researches per- 

 formed subsequently to those of Hales and Duhamel 2 . Thus if two saw- 

 cuts are made one above the other on opposite sides of twigs of the oak or 

 fir, each passing the centre of the stem, sufficient water still reaches the 

 leaves to keep them turgid. By using coloured solutions the curved paths 

 which the water follows may be made visible. If however, as in Ficns 

 elastica, lateral communications are imperfectly developed, cutting in this 

 manner may cause the leaves to become flaccid 3 . 



The elongation of the conducting elements usually causes the trans- 

 ference of water to take place preferably in the longitudinal direction, as 

 is shown by appropriate researches with coloured solutions 4 . For these 

 and other reasons the transference in the oblique direction is somewhat 

 more difficult, and hence the leaves wither when a large number of 

 alternating cuts are made one above the other on an oak branch. 



Experiments with coloured solutions. To determine the channels by which 

 water travels, coloured solutions have been employed since the time of Magnol 

 (1709) and de la Baisse (1733). Later still substances were employed by Unger, 

 Rauwenhoff, &c., whose presence could be detected by means of reagents 5 . Un- 



1 Russow, Bot. Centralbl., 1883, Bd. xin, p. 134; Schwendener, 1. c., 1892, p. 938 ; Strasburger, 

 1. c., 1892, pp. 473, 768 ; 1893, pp. 25, 82, &c. 



2 Lit. by Strasburger, Ban u. Verricht. d. Leitungsbahnen, 1891, p. 595. On herbaceous plants 

 cf. Haberlandt, Physiol. Anat, 1896, p. 322. 



3 Strasburger, Saftsteigen, 1893, p. 34. 



. 4 Th. Hartig, Bot. Zeitung, 1853, p. 313; Wieler, Forst- u. Jagdzeitung, 1891, p. 278; Stras- 

 burger, 1. c., 1891 ; K. E. F. Schmidt, Abhandlungen d. Naturf.-Ges. z. Halle, 1893, Bd. XIX, p. 85. 

 Other experiments in this direction are given by Wiesner, Unters. iiber d. Bewegung d. Imbibitions- 

 wasser, 1875, p. 10, &c. (Sep.-abdr. a. Sitzungsb. d. \Vien. Akad., 1875, Bd. LXXII, Abth. i). 



5 Cf. Treviranus, Physiol., 1835, Bd. I, p. 285 ; Mohl, Zelle, 1851, p. 73 ; Sachs, Gesch. d. Bot., 

 I 875, p. 522 ; Strasburger, Bau u. Verricht. d. Leitungsbahnen, 1891, p. 555. 



