412 M. Duchartre on the Anatomy and Organogeny 



of the ligneous zone, and comprised between the pith and this 

 ligneous zone. It is these vessels which in the ordinary Dicotyle- 

 dons belong to the form designated by the name of true spiral 

 vessels or of unrollable spiral vessels, and it is in this position 

 alone that these vessels are found in the stem. Here nothing 

 similar occurs ; the vessels nearest to the pith consist of finely re- 

 ticulated vessels, similar, although finer, to those which exist in 

 the rest of the ligneous layer. There are no tracheae with a con- 

 tinuous free and unrollable spiral fibre. 



This character, however, although forming an exception to 

 the most usual organization of dicotyledonous plants, is met with 

 in other vegetables of this class, and particularly in most parasi- 

 tical plants, although the unprecise manner in which authors ap- 

 ply the word spiral vessels may sometimes leave a doubt on this 

 point. 



A second remarkable character of the ligneous body of this 

 plant consists in the complete absence of medullary rays. This 

 fact is well established by M. Duchartre, and is placed beyond all 

 doubt. The ligneous zone is entirely formed of cells elongated 

 in the longitudinal direction of the stem and consequently parallel 

 to the pith, intermixed with more or less finely reticulated vessels, 

 and thus appearing most frequently radiated or punctated ; it is 

 not interrupted at any point by those lines of cells in a radiating 

 direction, which, extending from the pith toward the bark, con- 

 stitute the medullary rays. 



An analogous structure had been already noticed by M. Bron- 

 gniart in a family very far removed from the Lathracs, in the 

 Crassulacece *, in which the ligneous zone is equally unfm'nished 

 with medullary rays, and is only constituted of tissues elongated 

 in the direction of the axis and perfectly continuous. 



Having desired to ascertain whether, in the family to which the 

 Lathraa clandestina belongs, this character was found in any other 

 plant, we found that the Melampyrum sylvaticum presented the 

 same continuity in the elongated tissues of the ligneous zone, and 

 that there was also a complete absence of medullary rays. 



We thus find in several Dicotyledons an organization of the 

 stem which we were far from suspecting some years ago, and which 

 deserves the attention of physiologists. 



The bark presents, in its elongated internal tissue forming the 

 liber, the same continuity, in consequence of the absence of the 

 medullary rays which ordinarily extend from the wood into the 

 bark. The tissue which constitutes this internal cortical layer 

 has the greatest analogy with that which forms the non-vascular 

 part of the ligneous zone ; only it is more opake and more solid 



* See " Observations on the Internal Structure of the Sigillaria elegans," 

 &c.,by M. Ad. Brongniart. (Archives du Museum, tome i, p. 437.) 



