DIRECTION OF CELL-DIVISION. 



381 



According to him, the planes of the walls at a point of growth 

 may be thus classified : l 



r 





167 



1 " The relations of the periclinal and anticlinal planes are illustrated by 

 the following cases : 



(a) If the outline (in longitudinal section) of the growing point is a parab- 

 ola, the periclinals will constitute a system of confocal parabolas of different 

 parameter, the focus of the system being at the point of intersection of two 

 lines, of which one is the direction of the axis and the other of the parameter. 

 In this case the anticlinals, being the orthogonal trajectories of the periclinals, 

 constitute a system of confocal parabolas, the axis and focus of which coincide 

 with those of the periclinals. 



(b) If the outline of the growing point is a hyperbola, the periclinals will 

 be confocal hyperbolas, with the same axis but different parameter ; the anti- 

 clinals will be confocal ellipses, with the same focus and axis as the periclinals. 



(c) If the outline of the growing point is an ellipse, the periclinals will be 

 confocal ellipses ; the anticlinals will be confocal hyperbolas" (Abstract from 



FIG. 1G7. Tradescantia Virginica. Process of cell-division in the stamen-hairs. 

 , with a quiescent nucleus in the lower cell, and in the upper, one which has just fin- 

 ished its division ; b, nucleus showing a coarse granular structure with a tendency to 

 linear arrangement of the particles. The drawings from c to k inclusive exhibit the 

 different stages of cell-division at the following points of time: c, at 10 o'clock and 10 

 minutes; d, 10.20; e, 10.25; /, 10.30; r/, 10.35; Ji, 10.40; i, 10.50; j, 11.10; k, 11.30. 

 (Strasburger. ) 



