viTi] OF SIGMOID PARTITIONS 575 



everywhere at right angles: provided we continue to suppose that 

 the walls of the mother-cell (hke those of our diagrammatic /cube) 

 have become practically rigid before the partition appears, and are 

 therefore not affected and deformed by the tension of the latter. 

 In such a case, and especially when the cell is elliptical in cross- 

 section or still more comphcated in form, the partition may have 

 to assume a complex curvature in order to remain a surface of 

 minimal area. 



Fig. 226. S-shaped partitions: A, Taonia atomaria (after Rcinke); B, paraphya 

 of Fucus; C, rhizoids of moss; D, paraphyses oi Polytrichmn. 



While in very many cases the partitions (like the walls of the 

 original cell) will be either plane or spherical, a more complex 

 curvature will sometimes be alssumed. It will be apt to occur when 

 the mother-cell is irregular in shape, and one particular case of 

 such asymmetry will be that in which (as in Fig. 227) the cell has 

 begun to branch before division takes place. And again, whenever 

 we have a marked internal asymmetry of the cell, leading to irregular 

 and anomalous modes of division, in which the cell is not necessarily 

 divided into two equal halves and in which the partition-wall may 



