103 
ened his position by showing that the cells of the endosperm in 
the Gymnosperm Ceratozamia, divide with the reduced number. 
But it was Strasburger (1894) who proved it, beyond doubt, by 
showing that in the fern Osmunda 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 waa here, if 
anywhere, we must look for the tetrads. 
A. Material and Fixation—Two fern species (Preris tremula and 
Adiantum cuneatum) 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 1, 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 paraffine and cut horizontally in 
sections about 4 to 5 » thick. The stains used were Heidenhain’s 
haematoxylin, either alone or with orange G or Congo red as 
counter stains in the majority of ad eel orem 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). 1. A “ di- 
vision period,’ during which the primordial germ cells («« oégonia” 
and spermatogonia”) increase by ordinary mitoses; 2, a 
“ growth-period,” during which the primordial germ cells enlarge 
=e during which tetrads are formed. These cells are known as 
“primary odcytes” and “ primary spermatocytes,’ and 3, the 
“‘maturation-period,’ during which the nuclei with tetrads are 
divided by mitosis into nuclei with dyads (‘« secondary odcytes ” 
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 sixteen so-called “ spore-mother-cells ” in each spor- 
