88 



G. F. PAPENFUSS 



In the brown algae having an alternation of generations, mei- 

 osis occurs in the unilocular sporangia which are formed by the 

 diploid asexual generation. The haploid spores that are later 

 formed in these sporangia produce gametophytic plants, which 

 may be isogamous, anisogamous or oogamous (fig. 5). In the 

 Heterogeneratae, the gametophytes are filamentous and micro- 



DZOTXDTAISS 

 (oog.) 



TIL0PTBRIIUI23 

 (oog.T) 



CTJTI2RIAUS 

 (anlsog.) 



I 



C6S1URBSTIAISS IJUIINARIAI2S FT7CAISS 

 (oog.) (oog.) (oog.) 



8P0R0CHHAISS 

 (oog.) 



4 



CHORDARIALES 

 (tsog.-anisog.) 



SPHACBIARHIBS 



( l90&«nlsog?-oog^ 



DICTTO- 



SIPBOHiUES 



(ISOgrttnlMgJ 



HtFLOSTICHIHBAg POLSSTICglHBAB 



SCTOCARFALES 

 (taog.-anlsog.) 



t 



ISOCaMBftATAB HETEROCaareRATA« 



zz 



CICIO3P0H8*« 



\ 



Fig. 5 — Diagrammatic representation of the probable interrelationships of 

 the orders of the Phaeophyta. 



scopic; and in two of the orders, the Chordariales and the Dictyo- 

 siphonales, the zygotes usually produce filamentous plantlets 

 which resemble the gametophytes. These diploid filaments direct- 

 ly form new sporophytes as lateral outgrowths or they form 

 plurilocular sporangia whose zooids in turn give rise to filamen- 

 tous stages; and in certain instances several generations of such 

 plantlets (plethysmothaUi) may be produced. 



In many members of the Ectocarpales, Sphacelariales, Chor- 

 dariales and Dictyosiphonales, the sporophytes also form pluriloc- 

 ular sporangia. No meioses occur in these sporangia. The diploid 

 zoospores that are produced in them serve as accessory reproduc- 

 tive cells of the asexual generation. In the Chordariales and Die- 



