VIII] OF SIGMOID OR S-SHAPED PARTITIONS 355 



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

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

 curvature will be assumed under a variety of conditions. It will 

 be apt to occur, for instance, when the mother-cell is irregular in 

 shape, and one particular case of such asymmetry will be that in 

 which (as in Fig. 143) the cell has begun to brahch, or give ofE a 

 diverticulum, before division takes place. A very complicated 

 case of a different kind, though not without its analogies to the 

 cases we are considering, will occur in the partitions of minimal 

 area which subdivide the spiral tube of a nautilus, as we shall 



C D 



Fig. 142. S-shaped partitions: A, from Taonia atomaria (after Reinke); B, from 

 paraphyses of Fucus; C, from rhizoids of Mossj D, from paraphyses of 

 Polytrichum. 



presently see. 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 assume an 

 oblique position, then apparently anomalous curvatures will tend 

 to make their appearance*. 



Suppose that a more or less oblong cell have a tendency to 



divide by means of an oblique partition (as may happen through 



various causes or conditions of asymmetry), such a partition will 



still have a tendency to set itself at right angles to the rigid walls 



* Cf. Wildeman, Attache des Clo sons, etc., pis. 1, 2. 



23—2 



