SPIROGYRA 129 



Of the 2 species with semireplicate end walls, conjugation is scalariform 

 in I, and unknown in the other. 



Of the 65 species with repHcate end walls, the usual mode of conjuga- 

 tion is scalariform in 33, scalariform and lateral in 25, and lateral 

 in 6. Conjugation is unknown in i species. 



Reproduction by zygospores alone occurs in 242 species; by both aplan- 

 ospores and zygospores in 25 species; and by aplanospores alone in 

 8 species. 



Conjugating tubes are formed by both gametangia among plane-walled 

 species in 182; among semireplicate species in i; and among rep- 

 licate-walled species in 55. 



Conjugating tubes are formed by the male gametangia in 25 plane- 

 walled species, and in 12 replicate species. In several other species 

 with inflated receptive gametangia, they appear to be formed by the 

 male gametangia when seen in mature condition only. 



A majority of the species with male conjugating tubes have short repro- 

 ductive cells and longer vegetative cells alternating singly or in 

 pairs in the filaments. The reproductive cells (pro-gametangia) 

 can be distinguished readily before conjugation by their dark green 

 color and dense cell contents. The vegetative cells have thin light 

 green chromatophores and very transparent cytoplasm. Similar 

 cell differences also characterize species of Temnogametum and 

 Sirogonitim. In all these species there is an evident transfer of food 

 substances from the vegetative to the reproductive cells, before the 

 initiation of conjugation or spore formation. 



Spores are basically ellipsoid in 155 species; ovoid in 77; varying from 

 ellipsoid to ovoid in 13; and more or less compressed-globose to 

 lenticular in 30. 



Of the 25 species known to produce both zygospores and aplanospores, 

 7 occur among the plane-walled species, and 18 among the replicate 

 species. 



Key to the Species of SPIROGYRA 



I. Reproduction by zygospores 2 



I. Reproduction by aplanospores (zygospores unknown or rare) 183 



2. End walls of cells all plane 3 



2. End walls of cells distinctly and 



uniformly colligate i57- '5'. colli gata 



2. End walls of cells semireplicate 132 



2. End walls of cells replicate (in fruiting filaments many 

 plane) 134 



