576 



THE FORMS OF TISSUES 



[CH. 



assume an oblique position, then equally anomalous curvatures will 

 tend to make their appearance*. 



Suppose an oblong cell to divide by means of an obhque 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 of the mother-cell : and it follows that our oblique 

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

 complex, saddle-shaped or anticlastic surface. 



Many such partitions of complex or double curvature exist, but 

 they are not always easy of recognition, nor do they often appear 

 in a terminal cell. We may see them in the roots (or rhizoids) of 



t 



" 



A B C D 



Fig. 227. Diagrammatic explanation of S-shaped partition. , 



mosses, especially at the point of development of a new rootlet 

 (Fig. 226, C); and again among mosses, in the "paraphyses" of the 

 male plants (e.g. in Polytrichum), we find more or less similar 

 partitions (D). They are frequent also among Fuci, as in the hairs 

 or paraphyses of Fucus itself (B). In Taonia atofnaria, 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. 226, 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 



* Cf Wildeman, Attache des cloisons, etc., pis. 1, 2. 

 f Nova Acta K. Leop. Akad. xi, 1, pi. iv. 



