PERICLINES J ANTICLINES ; TRAJECTORIES. 



439 



the plant gives the impression of having been produced from dichotomously branched 

 cell filaments, whereas this subjective impression is not produced by the left side of 

 the figure — unless by peculiar modes of thinking. 



From reasons which will become clear in the further course of the exposition, 

 I distinguish all those cell-walls, or directions of cell-walls, which run conformably 

 with the circumference of the part of the plant under consideration, as Periclines, 

 in contrast to the Anticlines which are directed towards the circumference, or actually 

 cut it, and these terms are now introduced generally into botanical phraseology. 

 The periclines of our figure are therefore, according to what has been said above, 

 usually orthogonal trajectories of the anticlines. 



Without too great theoretical difficulties, now, we may suppose the above figure 

 to be the transverse section of an irregularly grown woody body. In this case the rows 

 of cells lying at the margin, and alone 

 bringing about the growth in surface, 

 would correspond to the wood-cam- 

 bium. The cells proceeding from the 

 peripheral layer would then be de- 

 veloped as wood-cells. As in the case 

 of the Alga, so also the wood-cells ex- 

 hibit no growth to speak of when they 

 pass over from the cambial or embry- 

 onic condition into their definitive form : 

 the arrangement of the cells produced 

 by the growth and cell-division in the 

 cambium likewise undergoes, therefore, 

 essentially no alteration. The processes 

 of cell-formation in the cambium of 

 wood, so far at least as the transverse 

 section is concerned, are made evident, 

 however, not merely in the individual 

 cells, but also in quite the same sense in 

 the annual rings of the wood and in the 

 medullary rays or ' silver grain ' which 

 traverse them. The annual rings appear here as periclinal layers of the mass of wood, 

 the medullary rays as anticlinal lines of cells representing the orthogonal trajectories 

 of them. If, as is the case with the inner annual rings in Fig. 274, the mass of wood is 

 nearly circular in transverse section, the annual rings, if of equal thickness all round, 

 form concentric circles, and the medullary rays then appear as radial lines, since they 

 cut these circles at right angles. The figure shows, however, how the woody body has 

 grown continually more irregular with increasing age : the annual rings (periclines) 

 having grown much more in thickness towards the side a, than on the side /. Finally, 

 by a wound, the formation of wood had ceased at a, while it proceeded only so much 

 the more vigorously at the margins of the wound m, n, p. In accordance with the 

 course of the periclinal layers of wood thus produced, the medullary rays directed 

 as anticlines have also now assumed other directions, so that they everywhere cut the 

 annual rings or periclines at right angles. The peculiar and very various curvatures 



Fig. 274.— Transverse section of the wood of a cherry stem 

 intis cerasifera) which had been deprived of its cortex on the 

 years previously, whence prominences had been produced 

 at m n f>. The thick radial lines are fissures produced by the drying 

 of the wood : their course follows the same law as the medullary 

 rays represented by thin lines. 



(Pru. 



siden 



