No. 463.] STUDIES ON PLANT CELL.— VI. 493 
formed prematurely during the heterotypic as was first described 
by Grégoire ('99). However, Grégoire and most botanists have 
considered the split between the V's as a second longitudinal 
fission of the original spirem in the spore mother-cell while 
Farmer and Moore regard it as the reappearance of an original 
single fission. This view of Grégoire, which has had the sup- 
port of Guignard ('99), Strasburger (: 00), and Mottier (:03), is 
the theory of a double longitudinal splitting of the chromosomes 
previous to the heterotypic mitosis and is also maintained in 
Allen’s (: 05) recent paper. 
The homotypic mitosis brings about the final separation of the 
arms of the V-shaped longitudinally split univalent (sporophytic) 
chromosomes of the heterotypic division. The fact that the 
arms of these V's finally break apart at the ends does not con- 
stitute'a transverse division as has been claimed by some earlier 
writers (Ishikawa, '97; Calkins, '97; Belajeff, '98 ; Atkinson, 
’99, for Trillium). The peculiarities of the homotypic mitosis 
are then due to the premature fission of the univalent chromo- 
somes during the heterotypic. As a type of nuclear division the 
homotypic mitosis is not fundamentally different from the typi- 
cal divisions of other periods of the life history. All recent 
authors are in agreement on this interpretation of the events of 
the homotypic mitosis. 
Gregory (:04) gives an account of sporogenesis for several 
leptosporangiate ferns and accepts Farmer and Moore’s explana- 
tion of reduction phenomena. He finds the same sort of U- 
shaped segments in the reduced number at the heterotypic 
division and considers them bivalent chromosomes which divide 
transversely so that the original sporophyte chromosomes are 
distributed in two sets during this mitosis. The various posi- 
tions assumed by the limbs of the U-shaped segments give 
appearances very similar to the tetrads described in the hetero- 
typic mitosis of animals and which Calkins (97) reported for 
Pteris and Adiantum and regarded as resulting from the trans- 
verse division of the halves of a longitudinally split chromosome. 
Gregory of course cannot accept the conclusions of Calkins. 
Williams (:04a) applies the theory of Farmer and Moore 
respecting the bivalent character of the chromosomes in the 
