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ened his position by showing that the cells of the endosperm in 

 the Gymnosperm Cemtozaniia^ divide with the reduced number. 

 But it was Strasburger (1894) who proved it, beyond doubt, by 

 showing that in the fern Osvmnda all the cells of the prothallus 

 have the reduced number of chromosomes ; in other words that 

 all cells derived from the spore have half as many chromosomes 

 as the cells of the asexual generation. Reduction in ferns, there- 

 fore, takes place during the formation of the spore and here, if 

 anywhere, we must look for the tetrads. 



A. Material and Fixation. — Two fern species {Pteris treniula and 

 Adianttnn aineatnni) were selected, which were found in a fernery 

 in October, to be in various stages of spore-formation. The pin- 

 nae were removed and cut into small pieces before fixation. The 

 fixing agents used were i, Herman's platino-aceto-osmic mixture; 

 2, Von Rath's fluid ; 3, corrosive sublimate ; 4, sublimate-acetic; 

 and 5, picro-acetic. The best results were obtained with i, 3 and 

 4. The pieces were imbedded in parafifine and cut horizontally in 

 sections about 4 to 5 p. thick. The stains used were Heidenhain's 

 haematoxylin, either alone or with orange G or Congo red as 

 counter stains in the majority of preparations, although Flemming's 

 triple stain gave good results. 



B. Terminology. — In animals three periods are recognized in 

 the development of the reproductive cells (O. Hertwig). i. A " di- 

 vision period," during which the primordial germ cells ('• obgonia" 

 and "spermatogonia") increase by ordinary mitoses; 2, a 

 " growth-period," during which the primordial germ cells enlarge 

 and during which tetrads are formed. These cells are known as 

 •* primary oocytes " and " primary spermatocytes," and 3, the 

 " maturation-period," during which the nuclei with tetrads are 

 divided by mitosis into nuclei with dyads (" secondary oocytes " 

 and " secondary spermatocytes"). These are again divided to 

 form eggs or spermatids. 



As regards the periods of maturation it can now be shown 

 that both male and female cells in many animals, and reproductive 

 cells in some plants (Pteridophytes), conform to the same type. It 

 is well known that in spore formation of Pteris , the single primor- 

 dial cell ultimately gives rise to sixty-four spores. It is also known 

 that there are si.xteen so-called " spore-mother-cells " in each spor- 



