466 BOTANICAL GAZETTE [JUNE 
which recalls that of synapsis. This later stage of aggregation was 
figured and described by Miss Sargant (’96, ’97) as a “second 
synapsis;” and it is the stage described as synapsis by Ernst (’o2), 
who apparently did not see the synapsis stage, properly so-called. 
Those portions of the split thread which lie in the peripheral region 
of the nucleus at this stage consist of loops which originate in, and 
return to, the central mass. The number of such loops is twelve. 
Transverse segmentation now occurs by the breaking apart of each loop 
in its peripheral region; each chromosome when first formed has its 
ends, therefore, at the periphery, and its median portion involved in 
the apparently tangled mass in the center of the nucleus. This is the 
general rule; but sometimes a chromosome lies comparatively free 
from its fellows, so that it can be followed throughout its length. 
An arrangement of the spirem into loops just before segmentation 
has been found by Schaffner (’97) in the macrospore mother-cell of 
Lilium philadelphicum, and by Farmer and Moore (’03) in the heter- 
otypic divisions of both animals and plants; but, according to their 
descriptions, segmentation occurs somewhere in the central region of 
the nucleus, so that the peripheral portion of each loop becomes the 
central part of one of the newly-formed chromosomes. The looping, 
as they conceive it, is preparatory to the bending of each chromosome 
into two closely appressed arms, which are destined to be separated in 
the metaphases by a transverse fission. My figures agree with those 
of both Schaffner and Farmer and Moore as to the formation of the 
loops; but it is certain that in Zi/ium canadense a loop does not repre- 
sent that part of the spirem which is destined to form a chromosome; 
but that, on the contrary, the peripheral portion of the loop marks the 
region in which the separation between two adjacent chromosomes 
is to occur. The looping, therefore, has nothing to do with a folding 
or bending of the chromosome, which, in fact, according to my observa- 
tions, never occurs. 
It will be seen that each chromosome consists, from the time of 
its formation, of two portions, the products of a longitudinal split- 
ting, which are twisted about each other. This double nature per- 
sists throughout the period of shortening of the chromosomes, down 
to the time of separation of the daughter chromosomes in the meta- 
phases; the separation in the heterotypic division, therefore, is along 
the line of the longitudinal fission which the spirem underwent before 
its segmentation. 
My observations as to the history of the chromosomes after seg- 
