VIl] 



OF CELL-PARTITIONS 



303 



cell constitutes a spherical lens-shaped surface, set normally to 

 the adjacent walls. At the tips of the branches of many Florideae, 

 for instance, we find such a lenticular partition. In Dictyota 

 dichotoma, as figured by Reinke, we have a succession of such 

 partitions ; and, by the way, in such cases as these, where the 

 tissues are very transparent, we have often in optical section a 

 puzzling confusion of lines ; one being the optical section of the 

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

 of its outer edge to which we have already referred. In the 

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

 curve, but a little lower down, where the sides of the shoot are 

 approximately parallel, we have flat transverse partitions, at the 

 edges of which, however, we recognise a convexity of the outer 

 cell-wall and a definite angle of contact, equal on the two sides 

 of the partition. 



Fig. 110. Cells of Dictyota. 

 (After Reinke.) 



Fig. HI. 



Terminal and other cells 

 of Chara. 



In the young antheridia of Chara (Fig. 112), and in the not 

 dissimilar 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 develop- 

 ment, we should have to take into consideration 

 the different pressures exerted by the single 

 curvature of the cylinder and the double 

 curvature of its spherical cap (p. 221) ; and 

 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 exactly equalled but for the Fig- 112. Young 



, ,. . , . , . , . . antheridium of 



adaitionai pressure inwards which it receives Chara. 



