128 ZYGNEMATACEAE 



Spore form, spore size, and wall ornamentation in hybrid 

 zygospores are produced by the cytoplasm of the receptive gamete. 

 For example, in collections containing filaments of two species 

 interconjugating, the spore is always similar in form and approx- 

 imate size to that of the specific filament in which the spore is 

 formed. Hybridization between a species with plane-walled spores 

 and a species with ornamented spore walls results in plane-walled 

 or ornamented zygospores, depending upon the specific filament 

 in which the receptive gamete is located. These facts fit in with 

 observations on the movements of gametes during conjugation in 

 which the male gamete moves into and through the cytoplasm of 

 the female gamete and becomes enclosed by it. Thus the surface 

 of the female gamete alone underlies the spore wall during its 

 development. This is not interpreted as cytoplasmic inheritance. 

 More probably the factors for these qualities of the cytoplasm are 

 in the chromosomes. The cytoplasm is merely the mechanism by 

 which spore wall forms, sizes, and patterns are formed. 



The processes of gamete organization, movement, and union 

 usually occur during the night. To study the successive steps 

 through the microscope one must avoid subjecting the cells to 

 intense light and high temperatures during the observations. 

 Under these conditions the motile gametes may stop moving and 

 become lodged at the sides or ends of the receptive gametes. This 

 abnormal condition may be seen in published photographs of the 

 process. Observations are best made at short intervals by turning 

 the light on and oflf or by tilting the mirror backward and forward. 



Analysis of Characteristics of the 275 Species 

 OF Spirogyra Here Described 



Number of species with end walls plane is 208; semireplicate, 2; rep- 

 licate, 65. 



Extreme diameters of vegetative cells with end walls plane are 10-200/1; 

 semireplicate, 12-18/1; replicate, 8-61 /i. 



Number of chromatophores in species with end walls plane is i to 16; 

 semireplicate, i ; replicate, i to 4. 



Number of species usually having i chromatophore is 129; approx- 

 imately 2 to 5 chromatophores, 109; and 6 to 16 chromatophores, 37. 



Of the 208 species with plane end walls, the usual mode of conjugation 

 is scalariform in 166, scalariform and lateral in 26, and lateral in 10. 

 Conjugation is very rare or unknown in 6. 



