THALLOPHYTA— ALG^ 



49 



form a true tissue, but are bound together by a kind of inter- 

 cellular substance, or are surrounded by a common gelatinous 

 coating. Each row of cells grows by division of the terminal 

 one, which is sometimes much larger than the others. There 

 is no intercalary growth of the filament by division of any of 

 the other cells, though lateral branches may arise from them. 

 The successive cells of the row or rows constituting the thallus 

 communicate with each other by a kind of rudimentary sieve- 

 plate [fig. 798), though they can hardly be described as sieve- 

 tubes. 



Fig. 799. 



Fitj. 798. Semi-diagrammatic longitudiual 

 section of an old and stout portion of 

 Ceramium rubrum, showing continuity 

 between the protoplasmic contents of 

 the axial or central cells, a, a, at their ends ; and laterally with the cortical 

 cells, &, by protoplasmic threads, and also that of the cortical cells iiil^r ne 

 by threads radiating from the central mass in each cell. After T. Hick. 



Fig. 799. Procarp of one of the Bed Seaweeds, tr. Trichogyne. sp. 



Spermatia. The branch to the left bears a cluster of autheridia. After Kny. 



The flattened forms usually grow at their margins, new cells 

 arising from divisions in certain cells in definite positions 

 there. The characteristic colouring matter is red, and is found 

 in chromatophores in the cells. As in the last group, chloro- 

 phyll is present in addition to the phycoerythrine. 



The group is characterised by great peculiarity in its methods 

 of reproduction, which are both sexual and asexiial. 



The gametophyte bears sexual organs and gonidia, the latter 



