THE ORDER OF CELL-DIVISION 49 



the anticlinal walls at right angles to these will correspond geometrically 

 to a system of orthogonal trajectories (cf. Fig. 13). The same figure shows 

 the course of the guiding lines when the points of maximum and minimum 

 growth lie on the axis of symmetry. In the latter case (lower half of 

 Fig. 13) the arrangement corresponds to that in the shoot-apex and root- 

 apex (darker part of Fig. 12). In the root-cap the most active growth 

 takes place along the axis of symmetry, and this usually gives an 

 arrangement as in the upper part of Fig. 13. This was termed by Sachs 

 the conical, divergent, or coaxial type, whereas the common type is a 

 system of confocal layers. 



Similar arrangements may, however, be produced in different ways, 

 and various causes may induce displacements sufficient to modify or even 

 completely change the primitive construction l . 



1 See Sachs, I.e., 1878, p. 195 ; Schwendener, I.e., pp. 418, 430; Krabbe, Sitzungsb. d. Berl. 

 Akad., 1882, p. 1,093. 



PFEFFER. II 



