246 THE ALGAE 



the activity of peripheral cells in the cortex which give successive 

 strata that can be recognized in section. Although reduction of the 

 life cycle has gone still further, nevertheless nemathecia still appear 

 and these also were formerly regarded as a parasite to which the 

 name Sterrocolax decipiens was given. In this genus, however, there 

 is neither fertiHzation nor meiosis and only degenerate procarps 

 are formed; instead the nemathecia contain monospores that de- 

 velop as follows: the warts, which arise as small cushions from 

 superficial cells of the thallus, contain some cells that become flask- 

 shaped together with other cells possessing denser contents that 

 arise in groups at the upper ends of the filaments. These latter, 

 which probably represent degenerate carpogonia, form the genera- 

 tive cells and they give rise to secondary nemathecial filaments, the 

 apical cells functioning as monosporangia, the spores from which 

 give rise to prostrate discs. In Ahnfeldtia, therefore, the sporo- 

 phytic generation has been completely suppressed, and this modi- 

 fied life cycle should be compared with that of Lomentaria rosea 

 (cf. below) in European waters where the gametoph5^c generation 

 has been secondarily suppressed. The monospores have been inter- 

 preted as morphologically equivalent to either the carpospores or 

 the tetraspores, the latter interpretation being the one adopted in 

 this volume. 



Rhodymeniales 



The thallus of all species is based upon the multi-axial type 

 of construction. In some genera the central portion becomes hollow 

 and divided by septa. There is considerable variation in form from 

 flattened, membranous thaUi to softer, terete and more gelatinous 

 structures. The order has been monographed by Kylin. Small 

 auxihary cells are cut off" before fertilization from a branch derived 

 from the support cell. They develop considerably only after fertili- 

 zation has taken place: otherwise they remain in a vegetative 

 condition. The order comprises two families, the Rhodymeniaceae 

 and Lomentariaceae. In the Rhodymeniaceae the carpogonia! 

 branch is three-celled and after fertiHzation the gonimoblasts be- 

 come profusely branched, the branches being known as gonimo- 

 lobes, and nearly every cell gives rise to a carpospore. In the 

 Lomentariaceae the carpogonial branch is three or four-celled and 

 each gonomoblast gives rise to a single terminal carposporangium. 



