488 THE AMERICAN NATURALIST: | [Vor. XXXIX. 
smaller element. During this mitosis the ten double chromo- 
somes divide but the single chromosomes remain entire and 
either pass to one pole or the other or are left out in the forma- 
tion of the daughter nuclei. The explanation of these conditions 
must be that ten chromosomes of D. rotundifolia fuse with ten 
from D. longifolia leaving ten of the latter without mates. 
Rosenberg's last paper (:04b) on Drosera describes in consider- 
able detail the union of chromosomes in pairs in both species of 
Drosera during sporogenesis. The sporophytic chromosomes 
which at first are scattered throughout the nucleus in the early 
prophase of the first mitosis come together in pairs and unite so 
closely that there is hardly a trace of their dual nature in the 
resultant larger bivalent chromosomes, which are of course the 
gametophyte number. Rosenberg is very positive that the pairs 
of chromosomes are preliminary to a fusion and not the result of 
a fission of already reduced segments of a spirem thread. 
Rosenberg believes that the two halves of the bivalent chromo- 
somes are separated in the first (heterotypic) mitosis and that 
each splits lengthwise prematurely during the first mitosis in 
preparation for the second. The fused bivalent chromosomes 
then appear to divide twice longitudinally but the first division 
may be only a separation of the two sporophytic chromosomes 
that entered into the fused pair. 
We shall consider now the conclusions of Berghs and 
Grégoire of the Carnoy Institute, Louvain, whose publications 
have appeared practically simultaneously with some of those 
which we have just discussed. Berghs has published three 
papers (:04a, : 04b, : 05) treating of the early history of sporo- 
genesis in Allium, Lilium, and Convallaria, and concludes from 
a study of synapsis that the spirem immediately preceding the 
heterotypic mitosis arises from the close association, side by 
side, of two delicate threads. These threads are organized pre- 
vious to and during synapsis and their coming together brings 
about that contraction of the chromatic material characteristic 
of synapsis. The threads contain sporophytic chromosomes of 
the last mitosis in the archesporium. The apparent longitudinal 
fission of the spirem which precedes the heterotypic mitosis in 
the spore mother-cell is interpreted as being these two threads 
