CIRCULATION AND FORMATION OF WOOD IN PLANTS. 573 



periments yielding these adverse results conducted in unobjection- 

 able ways, the conclusion implied by them would negative the con- 

 clusions above drawn. But these experiments are no less objection- 

 able than those to which they are opposed. Such mineral matters 

 as salts of iron, solutions of which have in some cases been supplied 

 to the roots for their absorption, are obviously so unlike the mat- 

 ters 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, besides the dif- 

 ficulty that the mineral mordant contained by the dye is injurious 

 to the plant, the further difficulty 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 traceable. To 

 be conclusive, then, an experiment on absorption through roots 

 must be made with some solution which will not seriously inter- 

 fere with the plant's vital processes, and which will not have its 

 distinctive element left behind. To fulfil these requirements I 

 adopted the following method. Having imbedded a well-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 — having 

 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 supplied for its absorption a simple decoction of 

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

 harm, and which, 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. Being prepared 

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

 hours, one of the lowest leaves, expecting that the application 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 visible as dark 

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

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

 which 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 

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

 chloride of tin to the cut surfaces, the vessels assumed that purplish 



