542 



periments yielding these adverse results conducted in unobjectionable 

 ways, the conclusion implied by them would negative the conclusions 

 above drawn. But these experiments are no less objectionable than 

 those to which they are opposed. Such mineral matters as salts of iron, 

 solutions of which have in some cases been supphed to the roots for 

 their absorption, are obviously so unhke the matters ordinarily absorbed^ 

 that they are likely to interfere fatally with the physiological actions. 

 If experiments of this kind are made by immersing the roots in a 

 dye, there is, oesides the difficulty that the mineral mordant contained 

 by the dye is injurious to the plant, the further difficuhy that the 

 colouring matter, being seized by the substances for which it has an 

 affinity, is left behind in the first layers of root tissues passed through, 

 and that the decolorized water passing up into the plant is not trace- 

 able. To be conclusive, then, an experiment on absorption througn 

 roots must be made with some solution which wih not seriously m- 

 terfere with the plant's vital processes, and wliich will not have its 

 distinctive element left behind. To fulfil these requirements I 

 adopted the following method. Having imbedded a weU-soaked 

 broad-bean in moist sand, contained in an inverted cone of card- 

 board with its apex cut off for the radicle to come through — ha\ing 

 placed this in a wide-mouthed dwarf bottle, partly filled with water, 

 so that the protruding radicle dipped into the water — and having 

 waited until the young bean had a shoot some three or more inches 

 high, and a cluster of secondary rootlets from an inch to an inch 

 and a-half long — I supphed for its absorption a simple decoction of 

 logwood, which, being a vegetal matter, was not likely to do it much 

 harm, and whicli, being without a mordant, would not leave its sus- 

 pended colour in the first tissues passed through. To avoid any 

 possible injury, I did not. remove the plant from the bottle, but 

 slightly raising the cone out of its neck, I poured away the water 

 through the crevice and then poured in the logwood decoction ; so 

 that there could have been no broken end or abraded surface of a 

 rootlet through which the decoction might enter. Bemg prepared 

 with some chloride of tin as a mordant, I cut off, after some three 

 hours, one of the lowest leaves, expecting that the apphcation of the 

 mordant to the cut surface would bring out the characteristic colour 

 if the logwood decoction had risen to that height. I got no re- 

 action, however. But after eight hours I found, on cutting off 

 another leaf, that the vessels of its petiole were made visiljle as dark 

 streaks by the colour with which they were chai-ged — a colour differ- 

 ing, as was to be expected, from that of the logwood decoctioa, 

 wliich spontaneously changes even by simple exposure. It was then 

 too late in the day to pursue the observations ; but next morning the 

 vessels of the whole plant, as far as the petioles of its highest un- 

 folded leaves, were full of the colouring-matter ; and on applying 

 chloride of tJa to the cut surfaces, the vessels assumed that pui-pli^h 



