400 



THE FORMS OF TISSUES 



[CH. 



(1) Suppose, in the first place, that the axis of growth hes 

 symmetrically in one of the original quadrantal cells of a segmenting 

 disc ; and let this growing cell elongate with comparative rapidity 

 before it subdivides. When it does divide, it will necessarily do 

 so by a transverse partition, concave towards the apex of the 

 cell : and, as further elongation takes place, the cyUndrical 

 structure which will be developed thereby will tend to be again 

 and again subdivided by similar concave transverse partitions. 

 If at any time, through this process of concurrent elongation and 

 subdivision, the apical cell become equivalent to, or less than, 

 a hemisphere, it will next divide by means of a longitudinal, or 



Fig. 182. 



vertical partition ; and similar longitudinal partitions will arise in 

 the other segments of the cylinder, as soon as it comes about that 

 their length (in the direction of the axis) is less than their breadth. 

 But when we think of this structure in the solid, we at once 

 perceive that each of these flattened segments of the cylinder, 

 into which our cylinder has divided, is equivalent to a flattened 

 circular disc ; and its further division will accordingly tend to 

 proceed like any other flattened disc, namely into four quadrants, 

 and afterwards by anticlines and periclines in the usual way. 



und Wachsthum (Arb. d. botan. Inst. Wicrzburg, 1878, 1879). But Sachs's treat- 

 ment differs entirely from that which I adopt and advocate here : his explanations 

 being based on his "law" of rectangular succession, and involving compUcated 

 systems of confocal conies, with their orthogonally intersecting elhpses and hyper- 

 bolas. 



