356 



THE FORMS OF TISSUES 



[CH. 



of the mother-cell : and it will at once follow that our oblique 

 partition, throughout its whole extent, will assume the form of 

 a complex, saddle-shaped or anticlastic surface. 



Many such cases of partitions with complex or double curvature 

 exist, but they are not always easy of recognition, nor is the 

 particular case where they appear in a terminal cell a common 

 one. We may see them, for instance, in the roots (or rhizoids) 

 of Mosses, especially at the point of development of a hew rootlet 

 (Fig. 142, C) ; and again among Mosses, in the "paraphyses" of 

 the male prothalli (e.g. in Polytrichum), we find more or less 

 similar partitions (D). They are frequent also among many Fuci, 

 as in the hairs or paraphyses of Fucus itself (B). In Taonia 



" 



A B CD 



Fig. 143. Diagrammatic explanation of S-shaped partition. 



atomaria, as figured in Reinke's memoir on the Dictyotaceae of 

 the Gulf of Naples*, we see, in like manner, oblique partitions, 

 which on more careful examination are seen to be curves of 

 double curvature (Fig. 142, A). 



The physical cause and origin of these S-shaped partitions is 

 somewhat obscure, but we may attempt a tentative explanation. 

 When we assert a tendency for the cell to divide transversely to 

 its long axis, we are not only stating empirically that the partition 

 tends to appear in a small, rather than a large cross-section of the 

 cell : but we are also implicitly ascribing to the cell a longitudinal 

 polarity (Fig. 143, A), and implicitly asserting that it tends to 



* Nova Acta K. Leop. Akad. si, 1, pi. iv. 



