948 Davis.—A Comparison of the Reduction Divisions of 
traction, but there a^e here also indications that segmentation is about 
to take place. 
The chromosome segments of the spireme when first formed are some¬ 
times four to six times longer than they are broad and of slightly varying 
lengths even in the same nucleus, but as the process of chromatin con¬ 
densation continues they become much shorter and gradually approach 
uniformity of size. In consequence of this process of segmentation the 
arrangement of the fourteen sporophytic chromosomes on the spireme is 
always end to end (Figs. 15-17), but as the spireme becomes older groups 
of chromosomes are frequently detached from the main chain. Pairs of 
chromosomes are thus occasionally separated which take the form of rings 
(Fig. 18), probably because they formed two sides of a loop in the spireme. 
The chromosomes of Lamarckiana y like those of biennis , are, then, not 
grouped regularly in pairs during the prophases of the heterotypic mitosis 
as was the case in material of grandiflora studied by the writer (Davis, ’ 09 ). 
In that material a characteristic pairing of the chromosomes was found 
to result from the regular arrangement of the loops of the spireme by which 
adjacent chromosome segments in the chain were as a rule brought 
somewhat side by side, so that they remained united to form seven ring- 
shaped bivalent chromosomes. Such pairs or rings are not common in 
Lamarckiana, and as a rule the arrangement of the chromosomes is in the 
form of a single long chain or two or more shorter chains. 
This method of the organization of the chromosomes in Lamarckiana 
as segments of a univalent spireme placed end to end is therefore the same 
as the history described by the writer for biennis and grandiflora , and in 
this conclusion the present paper is in full agreement with the account of 
Geerts for Lamarckiana and with that of Gates for rubrinervis . 
The Heterotypic Mitosis. The arrangement of the chromosomes end 
to end in a single chain or in two or more shorter chains is frequently 
maintained through the prophases of the first, or heterotypic mitosis, 
although the chromosomes may be so closely grouped that it is difficult 
to follow them with precision. The cause of the intimate association of 
the chromosomes may readily be traced to the conditions of the second 
contraction from which the prophases develop, and where, as described 
above, the condensation of the chromosome segments appears to draw 
these elements together. This condensation continues throughout the 
prophases so that the chromosomes at the metaphase of this mitosis 
(Fig. 27) are very much smaller structures than the segments of the 
spireme from which they were derived (Figs. 15-21). As in biennis and 
grandiflora , the mature chromosomes are essentially similar to one another, 
and have usually the form of thickened V’s due to the bending of the 
chromosome segments of the spireme; they are not rounded structures such 
as have been described and figured by Gates and Geerts. 
