104 JOHN H. SCHAFFNER Vol. XXII, No. 4 



II. LOWER SEXUAL SERIES, WITH REDUCTION OF THE 

 CHROMOSOMES EITHER IN THE ZYGOTE, OR AT THE 

 END OF THE SEXUAL GENERATION JUST BEFORE 

 GAMETOGENESIS. 



2. The lowest sexual condition in which sexuality manifests 

 itself by the development of a passing state of attraction 

 between two morphologically similar mature cells or isogametes. 

 In the most primitive cases there is no apparent morphological 

 or physiological differentiation outside of the property of 

 attraction. 



Examples: Diatoms, Desmids, Sphasrella, Botrydium, Cla- 

 dophora, Ulothrix, Ectocarpus. 



Note: We may assume that there is a chemical or physical, 

 or perhaps it would be better to say a physiological difference 

 corresponding to female and male states. 



3. Development of a difference in size and sometimes color 

 of the gametes which in typical cases are ciliated, free-swimming 

 cells. 



Examples: Pandorina, Bryopsis, Codium, Spirogyra sp. 

 Note : Spirogyra shows a considerable degree of heterogamy 

 in its highest species. 



4. The stage of sexual evolution in which the gametes are 

 typically difl'erentiated as male and female with a decided 

 dimorphism, the sperm cell being ciliated and small with little 

 cytoplasm and food supply and actively motile after being dis- 

 charged from the gametangium, the egg cell being nonciliated 

 and comparatively large with abundant cytoplasm and food 

 supply and also discharged from the gametangium although 

 nonmotile. 



Example: Fucus evanescens. 



Note: Fucus also shows a dimorphism of the gametangia, 

 and belongs to a more advanced stage of sexual evolution, but 

 its female gametes represent a condition which is just a stage 

 below the final evolutionary development of sexual cells. 



5. The stage representing the attainment of typical female 

 and male, plant gametes, showing the normal primary sexual 

 dimorphism. Female gamete or egg — large, stationary (not 

 discharged from the gametangium), with abundant cytoplasm 

 and food supply ; male gamete or sperm — small, free-swimming 

 with cilia, and with a small amount of cytoplasm and food. 



Examples: Volvox, Sphaeroplea. 



