OF SAP IN PLANTS. 49 



proved ; therefore no siphon action had been exerted. On this 

 day the twig was analysed. The solution had not only ascended 

 to the upper end in the one part, but also descended in the other 

 part (at the water side), and indeed just to the surface of the 

 water ; it had penetrated farthest of all in the vascular part of 

 the outermost wood, which, at the upper part, was in contact 

 with the absorbing half of the shoot ; in the liber and bark it 

 fell about 1 inch short of this, while the inner wood, the medul- 

 lary rays, and the pith, did not react. The surrounding water 

 exhibited no reaction, which, it may be remarked in passing, 

 does not speak much in favour of the hypothetical "root-secre- 

 tion/' The half dipping in the saline solution, when examined 

 upwards, reacted most in the medullary sheath, and in the (two) 

 outer layers of wood ; also, however, in the liber and bark ; while 

 the inner (third) layer of wood and the pith had not conducted 

 so far. At the upper free and undivided extremity, the branch 

 reacted only at one side, that corresponding to the vessel con- 

 taining the saline solution ; therefore the solution had not 

 passed round by the top to descend into the other half (to the 

 water), but had gone over (in extremely small quantity) hori- 

 zontally from wood to wood further down. 



When the experiment was stopped sooner, in other cases, it 

 was found (June 12th) that the solution had merely ascended, 

 and not descended ; in another piece of a shoot, the solution had 

 descended half way in the water-half by the 15th of June. In 

 one case, when the experiment was kept in action longer, the 

 solution had descended \ an inch down below the level of the 

 water in the half dipping in the latter,- not, however, to the 

 highest of the little roots ; here also the water exhibited no re- 

 action ; in fact, the portion of the inner layer of wood here laid 

 bare by splitting the shoot had not conducted. 



Whether, in these cases, the absorption of the saline solution 

 took place through the roots, or also through the lowest exposed 

 portion of the inner layer of wood, it is certain that here again 

 the liber and bark were decidedly less concerned than the tra- 

 cheae of the wood, in the descent of the sap. It is seen that the 

 descending sap, when it ascended from the roots and penetrated 

 horizontally from wood to wood, avoided the medullary sheath, 

 while it was shown in previous experiments that it very readily 



SCIEN. MEM. Nat. Hist. VOL. I. PART I. 4 



