162 
Digby . — On the Archesporial and 
the pollen mother-cells of Allium tricoccum. She traces the parallel threads 
of the heterotype prophases, which she calls daughter halves of single 
somatic chromosomes, as originating from the vacuolization of the chromo- 
somes in the preceding telophase of the last division of the sporogenous 
tissue. The continuity can be followed during the interkinetal rest when 
the remains of the chromosomes of the telophase are visible as ladder-like 
structures. During synapsis the parallel spiremes approximate, resulting in 
a single thick spireme. Apparently she did not see the stages of conjunc- 
tion. She is of opinion that the radiating loops of second contraction 
represent somatic chromosomes joined end to end, and that they separate 
at the outer end. Thereupon an arm of a loop pairs with, and twists 
round, an arm of a neighbouring loop ; thus a bivalent is formed by A + B. 
No such proceeding has been seen in Osmunda . 
Summary. 
t. For the convenience of readers a glossary of terms consistently used 
throughout this paper is here given. 
c Thread ’ — the longitudinal half of an entire univalent spireme or 
chromosome. 
* Filament ’ — an entire univalent spireme, i.e. the spireme resulting 
from the parallel association of two half univalent spiremes or threads. 
‘ Strands’ — very fine strands of linin (i) connecting the several chromo- 
some segments of early telophase ; (2) transversely connecting [a) the indi- 
viduals of a pair of associating and dissociating threads, (b) the individuals 
of a pair of conjoining and disjoining filaments. 
‘ Association’ = the coming together in pairs, side by side, of two 
threads or half univalent spiremes to form the entire univalent spireme or 
filament, which becomes the univalent chromosome. 
‘ Fission’ —(f) the longitudinal separation of the entire univalent spireme 
into two threads or half univalent spiremes ; (2) the longitudinal separation 
of a univalent chromosome into two daughter chromosomes. 
‘ Conjunction ’ — the coming together in pairs of two entire univalent 
spiremes or filaments to form the bivalent spireme which becomes the 
bivalent or heterotype chromosome. 
‘ Disjunction ’ = (1) the separation of the bivalent spireme into two 
entire univalent spiremes, or (2) the separation of the bivalent or hetero- 
type chromosome into two entire univalent chromosomes. 
2 . Archesporial Divisions. 
The archesporial divisions of Osmunda are straightforward, and con- 
form to the scheme generally described for the somatic mitosis of plants. 
