222 THE CELL 



that the space occupied by the embryonic substance is partitioned 

 out, so that anticlinal and periclinal walls intersect at right angles. 

 This being granted, the network of cells in Fig. Ill may be con- 

 structed according to a well-known geometrical law. Let x x re- 

 present the axis, and y y the direction of the parameter, then all 

 the periclines, denoted by P p, form a group of confocal parabolas. 

 Similarly, all the anticlines, A a, form another group of confocal 

 parabolas, whose focus and axis coincide with those of the pre- 

 ceding group, but which run in the opposite direction. Two such 

 systems cut one another everywhere at right angles. 



"Let us now observe whether a median longitudinal section made 

 through a dome-shaped, and approximately parabolic growing- 

 point, does not present an arrangement of cells which corresponds 

 in all essentials with our geometric diagram. We see at once, if we 

 examine such a section, made from the growing-point of a Larch 

 for example (Fig. 112), that the internal structure is identical, if 



fn 



Fro. 112. -Longitudinal section through the growing-point of a winter bud of Abies 

 uttnota (x about 200) (after Sachs, Pig. 285): a apex of growing point; b b youngest 

 aves ; r cortex ; m pith. 



we disregard the two protuberances, b b, which interfere somewhat 



with the symmetry of the figure. These are young leaf-rudiments, 



ding off from the growing-point. We recognise at once the 



two systems of anticlines and periclines, which it can scarcely be 



ibted cut each other at right angles, as in the diagram ; that is 



to say, the anticlines are the right-angled trajectories of the peri- 



3hnes. As in the diagram, further, only a few periclines under 



e apex S run round the common focus of all the parabolas ; the 



ers, which come from below, only reach the neighbourhood of 



