CRYPTONEMIALES 



227 



the central threads form three-celled carpogonial branches, whilst 

 the outer threads develop into two-celled filaments that are 

 modified auxiliary cells. After fertilization the carpogonium and 

 the cell below it fuse together and send out a filament to the lower 

 cell of the auxiliary branch. Finally, all the auxiliary' and nutritive 

 cells fuse to give one long fusion cell from which very short 

 gonimoblast filaments grow out. In the tetrasporic plant there are 



B 



- -M 



f 



c^c5c:scfac5) F 



a e 

 '« « 



t UQDOfiQQQQtSlQQQQQ 



Fig. 150. Epilithon membranaceum. A, carpogonia ( x 360). B, conceptacle with 

 ripe carpospores ( x 240). C, young antheridial conceptacle ( x 510). D, mature 

 antheridial conceptacle ( x 426). E, tetraspores ( x 228). F, G, thallus construction 

 ( X 360). (After Kylin.) 



simple filaments which give rise to the tetrasporangia ana branched 

 sterile filaments that form the roof to the conceptacle by the process 

 of division and elongation, the original roof being cast off: finally, 

 a pore develops above each group of tetraspores. 



*CoR.\LLiNACEAE : CoralUna (coral). Fig. 151. 



Both this and the preceding genus are examples of the "fountain" 

 type of construction (cf. p. 212). In Epilithon the original 

 construction has been much modified because of its habit, but 

 it can be observed extremely well in CoralUna. The erect plants, 

 which are jointed, cylindrical or compressed, arise from calcified 

 encrusting basal disks or prostrate interlaced filaments. Branching, 

 which is frequent, is either pinnate or dichotomous. There is a 

 central core of dichotomously branched filaments with oblique 

 filaments growing out at the swollen internodes to form a cortical 



15-^ 



