326. THE MICROSCOPE. 



after trying experiments with leaves of different ages and 

 different characters, and with undeveloped axes, as well as 

 with axes of special kinds, that it became manifest that 

 the appearances presented by ordinary stems, when thus 

 tested, are in a great degree misleading. " If an adult shoot 

 of a tree or shrub be cut off, and have its lower end placed 

 in an alumed decoction of logwood, or a dilute solution 

 of magenta, 1 the dye will, in the course of a few hours, 

 ascend to a distance, varying according to the rate of eva- 

 poration from the leaves. On making longitudinal 

 sections of the part traversed by it, the dye is found to 

 have penetrated extensive tracts of the woody tissue ; and, 

 on making transverse sections, the openings of the ducts 

 appear as empty spaces in the midst of a deeply-coloured 

 prosenchyma. It would thus seem that the liquid is carried 

 up the denser parts of the vascular bundles, neglecting the 

 cambium layer, the central pith, and the spiral vessels of 

 the medullary sheath." This, however, is found to be only 

 partially true. " There are indications that while the layer 

 of pitted cells next the cambium has served as a channel 

 for part of the liquid, the rest has ascended the pitted 

 ducts, and oozed out of these into the prosenchyma around. 

 This is seen, if, instead of allowing the dye time for oozing 

 through the prosenchyma, the end of the shoot be just 

 dipped into the dye and taken out again, we find that, 

 although it has become diffused to some distance round 

 the ducts, it has left tracts of wood between the ducts 

 mentioned. Again, if we use one dye after another, a 

 shoot that has absorbed magenta for an hour and then 

 placed for five minutes in the logwood decoction, transverse 

 sections taken at a short distance from the end of the shoot, 

 show the mouths of the ducts surrounded by dark stains 

 in the midst of the much wider red stains. The behaviour 

 of these corresponds perfectly with the expectation that a 

 liquid will ascend capillary tubes in preference to simple 

 cellular tissue, or tissue not differentiated into continuous 



(1) "These two dyes have affinities fbr different components of the tissues, and 

 may be advantageously used in different cases. Magenta is rapidly taken up by 

 woody matter and secondary deposits, while logwood colours the cell-membranes, 

 and takes but reluctantly to the substances seized by magenta. By trying both 

 of them on the same structure, we may guard ourselves against any error arising 

 from relative combination." 



