8 



This vessel has the fibre developed in the manner already describ- 

 ed, and I consider it to be the one that is first formed in the bundle 

 of vessels of which it makes a part, and formed, not in the way we re- 

 cognize it, but has degenerated from a spiral by two or more coils be- 

 coming united in a ring, and the fibre between these so formed rings 

 becoming absorbed, as Mohl, Meyen, together with Schleiden,* have 

 described. It is to be observed, as the first vessel, in the youngest 

 parts of plants ; and I believe its presence alone indicates a low degree 

 of the organizing power, by its occurrence in Equisetum and Lycopo- 

 dium, where it is frequently without any other, and which plants, in the 

 ascending scale of vegetation, are almost the first that possess vascular 

 tissue : and that the spiral fibre occurring with the rings marks a 

 higher step in the scale of organizing power, that the true spiral more 

 so, and the reticulated and dotted mark the highest. This being the 

 order in which we find these several vessels placed in herbaceous 

 exogens, proceeding from within outwards, and also developed ; the 

 differences of structure of the several vessels being indices of the 

 vital energy of the plant, at the several periods of their development. 



In those vessels in which the annular or spiral character of the fi- 

 bre is more or less departed from, some curious modifications of the 

 above process are to be observed, as in the reticulated vessels, such 

 as are met with in the common balsam {Balsamina hortensis). The 

 commencement of the formation of the fibre in these vessels is marked 

 by the tendency of the granules to take a more or less spiral course ; 

 when it happens in the lines thus marked out that some one of the 

 granules becomes enlarged by new matter deposited about it, this 

 granule so altered becomes the point which gives an origin to another 

 fibre or branch, which becomes developed by the successive attrac- 

 tion of granules into bead-like strings, and takes a different direction 

 to the original fibre, forming a cross bar or ramifying, thereby caus- 

 ing the appearance by which this vessel is recognized. 



In the dotted or marked vessels,f the fibre scarcely presents any 



* Annates des Sciences Naturelles, Seconde Serie, iii. Botanique, 373. 

 f The author, from the great difference which is to be found in the dotted vessels, 

 has been induced to distinguish four kinds, sufficiently distinct from each other, and 

 which occur almost exclusively in particular classes of plants, and which are to he re- 

 cognized by the following characters. 



dots nlane i D° tte d vessel ; a long slender vessel found 



i p » '••* | in herbaceous Exogens. 



dots with cen- f Exogenic vessel ; a very short large ves- 

 Markings rounded (dott) ■ tral mark,.. ( sel, in woody Exogens. 



«.«,„„»,! ,•„ ~». i Endogenic vessel , a very large long ves- 



arranged in rows | » ^ Jn En( } ogen8 ^ £ few / erns . 



Markings linear Acrogenic or Scalariform vessel, in Ferns. 



