220 LATHR.EA. [BOOK i. 



which exist in the rest of the ligneous layer. There are no 

 tracheae with a continuous free and unreliable spiral fibre. 

 This character, however, although forming an exception to 

 the most usual organisation of dicotyledonous plants, is met 

 with in other vegetables of this class, and particularly in most 

 parasitical plants, although the unprecise manner in which 

 authors apply 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, constitute 

 the medullary rays. An analogous structure had been already 

 noticed by M. Brongniart in a family very far removed from 

 the Lathrsea, in the Crassulacese, in which the ligneous zone 

 is equally unfurnished 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 Lathrsea clandestina 

 belongs, this character was found in any other plant, it was 

 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. It 

 thus appears- that there exists in several Dicotyledons an 

 organisation of the stem which botanists were far from 

 suspecting some years ago, and which deserves the attention 

 of physiologists. (See the translation of Duchartre's paper in 

 the Annals of Natural History, vol. xv.) 



A great number of similar anomalies have now become 

 known to botanists, and will be found recorded, and some- 

 times figured, in the works of Decaisne, Adrien de Jussieu, 

 Ach. Richard, Gaudichaud and others, and in the Penny Cyclo- 

 paedia. They occur more especially among Soapworts (Sapin- 

 dacese) Chenopods, Nyctagos and Loranths; some of them 



