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SUMMARY. 
1. The spore maturation in Pteridophytes agrees step by step 
with the maturation of sexual cells in animals. 
2. As in animal maturation, the process of spore-formation can 
be divided into three periods of division, growth and maturation. 
The division-period is the interval between the archesporium and 
the sixteen-cell stage of the sporangium. The growth-period is the 
interval during which the sixteen cells enlarge and tetrads are 
formed. The smaturation-period includes the two successive divi- 
sions of the nuclei in the sixteen-cell stage, and the formation of 
the spores. 
3. Different terms are used to designate the cells in the differ- 
ent stages of maturation. Those of the “division-period” are 
known as the “ archesporial cells.” Those of the “ growth-period ” 
have hitherto been known as the “‘spore-mother-cells.” The term 
“spore-mother-cell’’ is, however, inaccurate and clumsy, and I 
Suggest the term primary sporocyte in its place, also secondary 
Sporocyde for the daughter-cells of the primary sporocyte. These 
are the mother-cells of the spores and by their subsequent division 
the sixty-four spores are formed. 
4. The “ growth-period”’ is the most important stage in matu- 
ration. It begins with a distinct enlargement of the cell. The 
chromatin then forms a delicate moniliform spireme before the 
nucieolus has disappeared. A much thicker spireme is subse- 
quently formed from the moniliform thread. The thickened spireme 
then splits longitudinally. It next breaks up into half as many 
double spireme-segments as there are chromosomes in the somatic 
cells ; each of these double elements forms a tetrad. 
5. Three types of tetrad-formation are found in each nucleus. 
These may be called the “rod type,’ the “ring type” and the 
“cross type.” In the first type the halves of the double spireme 
Segment are completely separated; in the second, the halves be- 
come separated in the center but remain connected at the ends; 
in the third type the halves become separated at the ends but re- 
main connected at the centre. 
6. In all three types the tetrads are finally formed by « a trans- 
verse division of the halves of the double spireme-segment, giving 
reduction in the Weismann sense. 
