No. 463.] STUDIES ON PLANT CELL.— VI. 489 
which are believed to have never actually fused during synapsis. 
The reduced number of segments derived from the spirem pre- 
ceding the heterotypic mitosis are then bivalent chromosomes 
composed ‘of pairs of sporophytic chromosomes lying side by 
side. The heterotypic mitosis distributes the sporophytic 
chromosomes in two sets resulting in a numerical reduction 
of their numbers by one half. It will at once be noted that 
while Berghs and Allen have independently arrived at similar 
conclusions respecting the structure of the chromosomes of the 
heterotypic mitosis there are some important differences in the 
mode of origin. Allen reports an. actual fusion of the two 
threads (paternal and maternal) during synapsis and a later 
fission of the spirem previous to the heterotypic mitosis. But 
the accounts of both authors have much in common in their 
interpretation of the structure of the spirem and chromosomes 
of the heterotypic mitosis which is fundamentally different from 
the accounts of Farmer and Moore, and Strasburger to be 
described later. j 
Grégoire (:04) in a general discussion of reduction phenom- 
ena confirms the observations of Berghs and takes a very posi- 
tive position against the interpretations of Farmer and Moore 
and Strasburger. The chief features of his conclusions are in 
harmony with the results of Allen. The sporophytic (somatic) 
chromosomes are believed to become associated in pairs by the 
application of two delicate threads throughout their length during 
synapsis. These threads are believed to retain their autonomy 
and never actually to fuse although they may come in close con- 
tact. Consequently the reduced number of chromosomes are 
pairs of sporophytic chromosomes which have retained complete 
independence. Allen, on the contrary, reports a complete union 
of the two threads involving the fusion of chromomeres in pairs 
and a later longitudinal division throughout its length of the 
single (fusion) spirem. Grégoire does not regard the heterotypic 
mitosis as a true nuclear division but as a special process designed 
to effect this numerical separation of the sporophytic chromo- 
somes and intercalated between typical mitoses, while Allen 
would apparently treat it as a true mitosis and regard the chro- 
mosome reduction as effected by the fusion of two sporophytic 
spirems during synapsis. 
