35.] 



CHAPTER II. THE TISSUES. 



193 



The tangential division of 

 the cambium-cells takes place 

 in a regular order, termed, in 

 honour of the discoverer, Samo's 

 law of cambial division. Each 

 cambium- cell divides into two 

 by a tangential (parallel to sur- 

 face of member) wall ; one of 

 these two cells remains meris- 

 matic, the other undergoes 

 further division, by a tangential 

 wall, into two which may be 

 either directly converted into 

 permanent tissue (either wood 

 or bast) or after having .under- 

 gone yet another tangential 

 division. When an addition is 

 to be made to the wood, the 

 outer of the two first-formed 

 cells remains merismatic, the 

 inner forming permanent tis- 

 sue ; when to the bast, it is the 

 inner of the two first-formed 

 cells which remains merismatic, 

 and the outer which is con- 

 verted into permanent tissue. 



Not only does the fa?cicular 

 cambium add secondary wood 

 and bast to the primary bundles 

 of the stem, but the interfasci- 

 cular cambium generally forms 

 (except Menispermaceae, Cu- 

 curbitacese, woody Piperaceae, 

 Aristolochia, Casuarina, and 

 some other plants, where it 

 only -'forms conjunctive tissue) 

 new secondary bundles between 



FIG. 145. Part of a transverse 

 section of a branch of Pinus sylves- 

 tris, illustrating the development of 

 tissue from the cambium: the lower 

 part of the section is the central 

 (wood), the upper the peripheral 

 (bast) : i initial layer (cambium pro- 

 per), on each side of which are still 

 young desmogen-cells in process of differentiation into either wood or bast; 1, 2, 3 young 

 xylem-tracheids, with developing bordered pits; fc cells of the bast-parenchyma with 

 brown contents; e sieve-tube with lateral siev.e-plate ; m a medullary ray, to which 

 additions are also made in the cambial region. (After Strasburger : x 540.) 



V. S. B. O 



