OF SAP IN PLANTS. 45 



a leaf, the solution was traced in the entire stem, chiefly in the 

 wood cells and isolated tracheae (unroUable spirals and dotted 

 vessels), which latter also contained a few air-bubbles at the same 

 time, 



Tropaolum majus, — After five days' absorption the solution 

 was found inside the intercellular passages of the rind and pith, 

 still more in the prosenchyma of the wood, and most of all in 

 some tracheae. 



Cucumis Melo. — After one day's absorption all the intercellular 

 passages, for several inches upwards and downwards in the stem, 

 were found filled with the saline solution, while the fluid cell- 

 contents themselves did not react; particular portions of the 

 (wood-) prosenchyma, and above all some of the large tracheae, 

 had also absorbed. 



The size of the vessels here permitted a decision, for this and 

 all other cases, of the question whether the blue reaction so often 

 observed in the interior of the exposed tracheae might not result 

 from the process of preparation, in short from the cutting of 

 the sections, since the knife might indeed readily spread reacting 

 fluids from the neighbouring prosenchymatous cells into the 

 open mouths of the vessels. If such were the case, if therefore the 

 reaction in the interior of the vessels were exclusively caused by an 

 unavoidable smearing at the time of the analysis, the blue vas- 

 cular points arising from the reaction would not, at all events, 

 always occupy the same place in a succession of transverse slices 

 from a stem where the course of the vessels was exceeding 

 straight. But this actually took place, and it follows beyond 

 doubt that the tracheae can in some cases take up and carry 

 forward fluids. 



Vitis vinifera. — Here again it was found that the fluid pro- 

 ceeded both downwards and upwards from the absorbing leaf 

 into the shoot bearing it, and in both cases in the same situation, 

 namely, chiefly in the medullary sheath and in the portions of 

 cellular tissue enveloping the liber-bundles on the inner side ; 

 apparently somewhat more had descended externally, and some- 

 what more ascended internally. 



Cucurbita Pepo, — This time a tendril, instead of a leaf, was 

 immersed in the solution, but it absorbed very little, probably 

 in consequence of continued wet weather. Analysis showed 



