VII] OF CELL-PARTITIONS 479 



shaped surface, set normally to the adjacent walls; and the centre 

 of curvature is the meeting-point of two tangents to the cone. We 

 find such a lenticular partition at the tips of the branches of many 

 Florideae; in Dictyota dichotoma, as figured by Reinke, we have 

 a succession of them. And by the way, where, in such cases as 

 these, the tissues happen to be very transparent, we often have a 

 puzzUng confusion of lines (Fig. 166); one being the optical section 



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Fig. 166. CeWs oi Dictyota. Fig. 167. Terminal and other cells 



After Reinke. of Chara. 



of the curved partition- wall, the other being the straight linear 

 projection of its outer edge to which w^ have already referred. In 

 the conical terminal cell of Chara, we have the same lens-shaped 

 curve; but a little lower down, w^here the sides of the shoot are 

 approximately parallel, we have flat transverse partitions, and the 

 form of the cells is, more or less, w^hat we have been led to expect 

 in the simple case of successive transverse partitions (Fig. 167). 



In the young antheridia of Chara (Fig. 168), and in the geo- 

 metrically similar case of the sporangium (or conidiophore) of 

 Mucor, we easily recognise the hemispherical form 

 of the septum which shuts off the large spherical 

 cell from the cylindrical filament. Here, in the first 

 phase of development, we should have to take 

 into consideration the different pressures exerted 

 by the single curvature of the cyUnder and the 

 double curvature of its spherical cap (p. 371) ; a id 

 we should find that the partition would have a 

 somewhat low curvature, with a radius less than 

 the diameter of the cylinder, which it would have Fig. 168. Young 

 exactly equalled but for the additional pressure anthendium of 

 inwards which it receives from the curvature of 

 the large surrounding sphere. But as the latter continues to 



