GIGARTINALES 



241 



nemathecia as belonging to a parasitic plant, which in this case was 

 given the name of Actinococcus subcutaneus, but it has since been 

 shown that we are really dealing with a parasitic diploid generation. 

 In the related genus Ahnfeldtia, 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 



B 



— s 



Fig. 161. Life cycles. A, Phyllophora viembranifolia. B, P. Brodiaei. C, Ahn- 

 feldtia plicata. 5 = nionospores. (After Svedelius.) 



neither fertilization nor meiosis and only degenerate procarps are 

 formed; instead the nemathecia contain monospores that develop 

 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 generative 

 cells and they give rise to secondary nemathecial filaments, the 

 apical cells of which function as the monosporangia. In Ahnfeldtia, 

 therefore, the sporophytic generation has been completely sup- 

 pressed, and this modified life cycle should be compared with that 



CSA 



16 



