492 THE AMERICAN NATURALIST. [VoL. XXXIX. 
The spirem thread thus breaks up into segments which, how- 
ever, lie in pairs represented by the V’s in the reduced (gameto- 
phyte) number. The pairs are bivalent chromosomes, each 
composed of two sporophytic chromosomes which were arranged 
serially on a single spirem thread. The pairs are not always 
organized through the approximation of the arms of V-shaped 
loops but this is a very characteristic type of structure. The 
V's have been interpreted by other authors as the approximation 
of portions of the spirem thread (Dixon, '95, '96, : 00) or the 
separation of their free ends at the bend of the loop as a trans- 
verse division of a reduced number of looped chromosomes in 
the heterotypic mitosis (Schaffner, ’97). The two parts of the 
bivalent chromosomes (which are pairs of somatic chromosomes) 
now become shorter and thicker and all trace of the original 
fission of the spirem thread is lost. 
The essential features of Farmer and Moore's interpretation 
of the prophase of the heterotypic mitosis are, then : (1) a sin- 
gle spirem with the sporophytic chromosomes arranged serially, 
which splits only once longitudinally, the fission afterward 
becoming obliterated when the chromosomes are organized, 
and (2) the organization of bivalent chromosomes in the reduced 
number largely by the approximation of the free ends of loops 
which entails a separation at the bend of the loops of the two 
sporophytic chromosomes, giving the appearance of a transverse 
division. 
The heterotypic mitosis, then, according to Farmer and 
Moore involves merely the distribution of the sporophytic chro- 
mosomes arranged in pairs (bivalent chromosomes) as univalent 
elements to each daughter nucleus. This is of course the gen- 
erat conclusion of all recent investigators, the different views 
being the result of varying accounts of the method of organiza- 
tion of the bivalent chromosomes. During this distribution in 
the heterotypic mitosis the split of the original spirem appears 
in each univalent element (sporophytic chromosome) and the 
halves open throughout the greater part of their length giving 
the peculiar V-shaped daughter chromosomes so characteristic 
of this mitosis in the lily. The arms of these V's become the 
daughter chromosomes of the homotypic mitosis which are thus 
