Gregory . — Spore-Formation in Leptosporangiate Ferns . 449 
somes move towards the equatorial plate — a longitudinal fission becomes 
once more clearly apparent in each limb (Figs. 24, 24 a), so that, seen 
in face, the diverging daughter- chromosomes form a ^-shaped body 
(Figs. 25, 26). This fission has been interpreted by many authors as a 
second longitudinal fission, appearing very early as a provision for the 
second maturation division. 
In the small chromosomes of the Ferns it is impossible in all cases 
to trace the presence of the original longitudinal fission through the late 
prophase condition up to the beginning of metaphase. Nevertheless, 
a study of the successive forms assumed by the chromosomes indicates 
that the gradual obliteration is apparent rather than real ; for it can still 
be recognized by means of the slightly bifid ends of the limbs of the 
chromosomes. These appearances are sufficiently convincing as to the 
correctness of the interpretation of the so-called second longitudinal fission, 
as nothing more than a reappearance of the original fission undergone by 
the spireme in the early stages of prophase. 
During anaphase the daughter-chromosomes preserve their V-shaped 
appearance (Fig. 27), and finally aggregate closely together at the poles 
of the spindle (Fig. 28), where they finally occupy a space resembling 
a vacuole in the cytoplasm (Fig. 29). 
This space appears to be bounded by a nuclear membrane, which, 
however, only persists for a very short time. The chromosomes fuse end 
to end in the manner described in several instances by Strasburger 1 , form- 
ing a thread which does not pass into a reticular structure (Fig. 29). 
The second (homotype) division follows very rapidly upon the com- 
pletion of the heterotype division, and is provided for by the longitudinal 
fission already noticed in the diverging chromosomes of the heterotype 
division (Figs. 30, 31). 
If, as seems likely, this fission is in reality that which appeared in the 
prophase of the heterotype division, the latter division may, as Farmer and 
Moore have pointed out, be considered a process intercalated between the 
earliest and the later stages of the homotype division. 
The result is then a transverse true reduction-division of the bivalent 
chromosomes which characterize the heterotype division. This work there- 
fore provides an extension to another group of plants of the results obtained 
by Farmer and Moore in certain plants and animals. 
4. General Considerations. 
In connexion with the segregation of characters, which takes place at 
the formation of the gametes in Mendelian hybrids, the occurrence of 
1 Strasburger, ’ 00 . 
