VIII] OF SIGMOID OR S-SHAPED PARTITIONS 357 



divide (just as the segmenting egg does), by a partition transverse 

 to its polar axis. Such a polarity may conceivably be due to 

 a chemical asvmmetry, or anisotropy, such as we have learned 

 of (from Professor Macallum's experiments) in our chapter on 

 Adsorption. Now if the chemical concentration, on which this 

 anisotropy or polarity (by hypothesis) depends, be unsymmetrical, 

 one of its poles being as it were deflected to one side, where a little 

 branch or bud is being (or about to be) given off, — all in precise 

 accordance with the adsorption phenomena described on p. 289, — 

 then our "polar axis" would necessarily be a curved axis, and the 

 partition, being constrained (again ex hyjpoihesi) to arise transversely 

 to the polar axis, would lie obliquely to the apparent axis of the 

 cell (Fig. 143, B, C). And if the obhque partition be so situated 

 that it has to meet the opposite walls (as in C), then, in order to 

 do so symmetrically (i.e. either perpendicularly, as when the 

 cell-wall is already sohdified, or at least at equal angles on either 

 side), it is evident that the partition, in its course from one side 

 of the cell to the other, must necessarily assume a more or less 

 S-shaped curvature (Fig. 143, D). 



As a matter of fact, while we have abundant simple illustrations 

 of the principles which we have now begun to study, apparent 

 exceptions to this simplicity, due to an asymmetry of the cell 

 itself, or of the system of which the single cell is but a part, are 

 by no means rare. For example, we know that in cambium-cells, 

 division frequently takes place parallel to the long axis of the 

 cell, when a partition of much less area would suffice if it were 

 set cross-ways : and it is only when a considerable disproportion 

 has been set up between the length and breadth of the cell, that 

 the balance is in part redressed by the appearance of a transverse 

 partition. It was owing to such exceptions that Berthold was 

 led to qualify and even to depreciate the importance of the law 

 of minimal areas as a factor in cell-division, after he himself had 

 done so much to demonstrate and elucidate it*. He was deeply 

 and rightly impressed by the fact that other forces besides surface 



* Cf. Protoplasmamechanik, p. 229: "Insofern liegen also die Verhaltnisse hier 

 wesentlich anders als bei der Zertheiluno; hohler Korperformen durch fliissige 

 Lamellen. Wenn die Membran bei der Zelltheilung die von dem Prinzip der 

 kleinsten Flachen geforderte Lage und Kriimmung annimmt, so werden wir den 

 Grund dafiir in andrer Weise abzuleiten haben." 



