uf the Stem uf the Phancruijainia. 399 



Schleideu does uot extend his researches (except in the case 

 of Draccena) to the examinatiou of the question how the cambium- 

 layer behaves in the stem after the unfolding of the bud, and 

 what becomes of it in the full-grown stem, of the Monocotyle- 

 dons. This point was taken up by Karsten {' Yegetationsorgaue 

 der Palmen,' 18i7). This author had the great advantage, in 

 his investigations made in the tropics, of possessing abundant 

 material, consisting of living and entire plants, — an advantage 

 which no one knows better how to value than myself, since, in 

 my ' Anatomy of the Palms,^ I was restricted for the most part 

 to isolated fragments of stems. 



Karsten explains most clearly how, in the terminal bud of the 

 Monocotyledons, especially of the Palms, the wood-bundles take 

 their origin in the cambial tissue of a hollow cone, the cambium 

 of the latter becoming converted in some places into parenchyma, 

 in others into the vascular-bundle tissue. With the progressive 

 development of the bud into a stem, the hollow cone assumes 

 at its lower end a cylindrical form. The increase of the cam- 

 bium endures in it for some time, while its outer, and more 

 particularly its inner surface, are simultaneously converted into 

 parenchyma — certain portions of the cambial cells at the same 

 time separating as it were from the parenchyma and becoming 

 developed into the woody bundles running into the medulla, 

 and in some plants also into the rind. After the various parts 

 of the stem have thus been produced from the cambium -cone, 

 the cell-producing energy is lost in the latter (except in the case 

 of the BraccBim), and the last remnants of the cambium undergo 

 a transformation into a layer organized somewhat differently in 

 different plants, which, in the full-grown stem, lies between the 

 internal vascular bundles and the rind, and is termed by Karsten 

 the wood-cylinder. In the Palms the cells of this wood-cylinder 

 agree closely with the cells of the rind and of the medulla ; and 

 in this way originates a tissue, analogous to the medullary rays 

 of the Dicotyledons, connecting the medulla and the rind. The 

 same condition occurs in the Pandanese, Aroidere, Oichidese, and 

 Grasses. In other plants the cells of the outermost layers of 

 the cambium assume forms which differ essentially from those 

 of the cells of the rind and medulla, especially by the great 

 thickening of their walls (lignification), and form a boundary- 

 layer between the medulla and rind, often consisting only of two 

 strata of cells. The forms of these cells are varied : where the 

 inferior terminations of the vascular bundles are connected to- 

 gether to form a reticulation, the cells are parenchymatous; 

 where the vascular bundles have a parallel course, they are more 

 or less prosenchymatous. The lignification of these cells induced 

 Karsten to name the layer they form the woody layer [Holzschicht), 



