Miscellaneom. 379 



and will then emit bubbles of air ; finally, the experiments cannot be 

 regarded as conclusive if made upon branches separated from the 

 trunk, as then the air would easily find its way into the vessels. 

 Nothing can be concluded from the circumstance that the walls of 

 these organs are not thickened by deposits, as many originally suc- 

 culent organic elements are in the same case. 



If liquids circulate in non-vascular plants, this only proves that 

 the vessels are not the sole organs of circulation ; and although 

 water charged with nutritive substances enters by spongioles which 

 contain no vessels, this does not prove that it does not penetrate 

 subsequently into the latter organs. 



As regards the course followed by the poUinic granules, no con- 

 clusion can be drawn from it, as there is not the least relation be- 

 tween the materials of fecundation and the sap. 



If we have no demonstration that the trachean vessels are exclu- 

 sively destined to the transport of gases, we find nothing more con- 

 clusive in the arguments advanced by Mirbel and Schultz, and other 

 authors, who hold the opinion that these vessels serve for the circu- 

 lation of liquids. They say that we see in them bubbles of air, 

 which would not be visible if they were not circumscribed by a 

 liquid — that the absorbed water diffuses itself so rapidly in plants 

 that it cannot but follow the direct courses presented by these con- 

 duits — that when the branch of a tree is placed in a coloured liquid, 

 the latter ascends in the vessels, into which it also penetrates even 

 when absorbed by the roots — lastly, that as the elaborated sap cir- 

 culates in the laticiferous vessels, the ascending sap must ascend by 

 analogous ducts, &c. 



But the liquids which surround the air-bubbles may have pene- 

 trated into the vessels when the observed tissues were cut into thin 

 sections ; those which ascend into the branches may be introduced 

 by the gaping orifices of section ; the colouring-matters which tinge 

 the vessels may only impregnate their walls externally ; lastly, 

 if it be true that the proper juices of certain plants move in true 

 vessels, it does not follow that there is anything analogous for the 

 ascending sap, or that it is the office of the trachean vessels to trans- 

 port it. 



Direct observation shows that at the earliest period of the forma- 

 tion of the tissues the trachean vessels are full of juices, like the 

 other organic elements, and that they are only deprived of these at 

 a later period. But even then they may be traversed by liquids of 

 considerable density. 



The wood of certain plants, such as Ulmus campestris, Uobinia 

 pseudo- Acacia, and Quercus Ilex contains large vessels, the interior 

 of which is occupied by a more or less consistent reticular tissue. 

 This tissue evidently could not have been produced unless the vas- 

 cular tubes had been filled with a liquid containing organic materials 

 in solution. 



Another observation proves that trachean vessels may contain 

 substances which become thickened so as to obstruct their cavity. 

 In a section of the stem of Calamus Rotang the author found, in 



