PH^EOPHYCE^E 113 



of being able to renew the apical cell after the 

 original one has perished. This property is akin 

 to another exhibited by the branches which bear 

 the gemmae and sporangia. After the fall of a 

 gemma, the remaining basal cells of the branch that 

 bore it may proceed to grow and form another one. 

 Similarly after the emptying of a sporangium, the 

 branch may grow through the membrane and form 

 a new sporangium. 



The branches are either all of equal morphological 

 value or there may be a distinction between 

 long and short ones. The latter are alternate in 

 Stypocaulon and Halopteris, opposite in Chcetopteris, 

 and in whorls in Cladostephus. They are either 

 themselves unbranched (Stypocaulon and Chcetopteris), 

 or branched on one side (Cladostephus), or they re- 

 semble in miniature the branching of the long 

 branches (Halopteris). In Stypocaulon y Cladostephus, 

 and not so markedly in Halopteris, the outermost 

 cells of the filaments of the thallus undergo farther 

 division and produce a cortical tissue of small cells 

 which obscures the articulation of the original thallus. 

 In Sphacelaria and Chcetopteris this articulation of 

 tiers of cells remains apparent throughout the life of 

 the plants. A farther modification takes place in 

 Cladostephus, Stypocaulon, Halopteris, and some 

 species of Sphacelaria by the outgrowth of rhizoid 

 filaments from the older parts of the shoots. These 

 filaments grow downwards, creeping over the thallus, 

 and form a kind of mantle over the lower parts of 

 the shoots. 



Some of the Sphacelariacece are subject to the 



I 



