TILOPTERIDALES (ISOGENERATAE) i6i 



possible that they represent a transition towards the tetrasporic 

 Dictyotales (cf. p. 163). The chief characteristic of the asexual plant 

 is reproduction by means of quadrinucleate monospores which may 

 be equivalent to unsegmented or primitive tetraspores, although 

 they might equally well be degenerate tetraspores. Sexual repro- 

 duction is brought about by means of gametes from microgametangia 

 and larger associated sporangia that may represent oogonia, but 



Fig. III. Haplospora globosa. A, portion of plant with uninucleate sporangia, 

 m (oogonia?), and plurilocular microgametangia, p. B, plurilocular micro- 

 gametangium. C, monosporangium with quadrinucleate monospore. D, mono- 

 sporangia. E, F, unilocular sporangia (oogonia?). (A-C, after Oltmanns, D-F, 

 after Tilden.) 



as fertiUzation has not been observed there is an opportunity here 

 for future research which should also determine whether there 

 is a regular alternation of generations. The evidence at present 

 available suggests that there is probably a regular alternation of two 

 similar generations. 



The sexual plants develop intercalary tubular microgametangia 

 which are produced by the transformation of one or more cells of 

 the main filament. Besides these organs there are the larger and 



CSA 



1 1 



