WALL STRUCTURE IN THICK CELL WALLS 103 



number of the filaments parallel to each other so that the diagram of 

 those branches which are not parallel (and whose diagram is therefore 

 spread over a circle) does not interfere. The X-ray diagrams of mature 

 specimens of the three species are almost identical and a typical 



1 



(b) 



Fig. 36. The development of a branch in a filament of Cladophora. Part of the wall 



at the end nearer the filament tip becomes "blown out" into a protuberance which 



then continues to grow like the apex of the parent filament, 



(o) The run of the striations on the outer wall lamellae at a branch (1) young stage, 



(2) older stage. 

 {b) Two views of the run of striations in inner lamellae, deposited after formation 



of the branch. 



The striations in (o) (1) suggest that the branch arises by a lateral "blowing out" 



of the wall. Layers deposited later are so adjusted as to give a smooth run of 



striations from the parent cell to the branch. 



example, obtained as usual with the beam normal to the length of the 

 filament, is given in Plate IV, Fig. 4. In order to achieve a clear inter- 

 pretation of this diagram, which will prove of material importance later 

 on, it will be as well to turn first to the species CI prolifera, whose cells 

 are large enough to be examined individually. When one of these cells 



