350 Mottier . — On the Prophases of the Heterotypic Mitosis in 
brought side by side by a looping or other form of approximation. Sub- 
stantially the same history of the origin of the bivalent chromosomes has 
been observed by Lewis (’ 08 ) for Pinus and Thuja. 
In a recent number of this journal, Overton (’ 09 ) has published the 
results of his latest observations on the heterotypic mitosis in the pollen 
mother-cells of Thalictrum pur pure scens , Calycanthus floridus, and Richardia 
africana . All of his data are interpreted in the light of the prochromosome 
theory and of the lateral union of two spirems prior to or during synapsis. 
In the pre-synaptic as well as post-synaptic stages he sees bivalent ‘ hetero- 
geneous ’ spirems, and the line of longitudinal fission of the post-synaptic 
spirem is regarded as the line of approximation of two spirems. I shall not 
discuss his data nor his deductions at this writing, except in so far as they 
pertain to Helleborus foetidus and P odophyllum peltatum. In his last, as in 
his preceding paper (’ 05 ), he cites Helleborus foetidus as revealing prochro- 
mosomes and a bivalent spirem in pre-synaptic nuclei (see his Figs. 39 to 43 
for Helleborus , and Figs. 53 and 54 for Podophyllum (l.c., ’ 05 ) ; also pp. 39 
and 47 (l.c., ’ 09 ). From a study of my numerous preparations of Helleboms , 
made from material fixed in several of the well-known fixing fluids, I may 
say with positive assurance that the pre-synaptic stages in the pollen 
mother-cells of this plant are quite similar to those described and figured 
by me for the pollen mother-cells of both Podophyllum and Lilium 
(Mottier, ’ 07 ). In fact, my Figs. 1, 2, and 4 of Podophyllum , and Figs. 16, 
17, 34, 19, and 20 of Lilium , are precisely like the corresponding stages in 
Helleborus , and might be readily substituted as illustrating the same 
conditions in the latter plant. In the very early stages of Helleboms , as in 
P odophyllwn and in Lilimn , there is no definite spirem, but a network or 
reticulum, consisting of chromatin lumps or granules of varying sizes and 
shapes connected by delicate linin strands. The number of these lumps 
always exceeds the number of somatic chromosomes. Some of these lumps 
are paired, as well as some of the linin strands ; but there are also clusters 
of three or more lumps, as well as three or more parallel linin strands 
connecting different lumps. There are also linin strands radiating or 
extending in several directions from some of the lumps. Just prior to 
synapsis in Helleborus , a definite slender spirem may be developed precisely 
as figured for Lilium Martagon (l.c., Figs. 19 and 20). As already stated 
for Podophyllum , in one end of the anther of Helleborus nuclei may show 
the structure of my Figs. 1 and 2 (l.c., ’ 07 ), while in the other end of the 
same loculus the chromatin is much more finely divided, as in Fig. 4 
(l.c., ’ 07 ). 
Judging from Overton’s figures of the pre-synaptic stages which he 
gives in his recent paper (l.c. ’ 09 ), it seems to me that he has failed to 
distinguish between a network and a spirem. The structure shown in his 
Figs. 1, 2, 3, 4, 5, 6, and 7 of PI. I, and Figs. 1, 2, 3, and 8 of PL II, for 
