172 BOTANICAL GAZETTE [SEPTEMBER 
Among those who are convinced of the bivalent character of the 
heterotype chromosomes, i. ¢., that this is a reducing division, two views 
are held as to the manner in which these chromosomes are formed. 
According to the view advanced by STRASBURGER (’o4) and FARMER 
(’os), the chromatin spirem splits longitudinally, the two segments 
or daughter spirems fusing again shortly afterwards, and segments 
into pieces equal to two somatic chromosomes placed end to end. 
Each piece, or double chromosome, folds, either during or after the 
cross segmentation, to form the familiar paired rods, rings, loops, 
etc., so often figured by the several observers. Consequently the 
two segments of each chromosome are not daughter chromosomes, 
formed by a longitudinal splitting, but two somatic chromosomes, 
each of which is split lengthwise; but, as stated above, this longi- 
tudinal split is not usually recognizable until the meta- or anaphase. 
Jures BErcHs (’o4, ’05) and other students of GREGOIRE assert that 
the longitudinal fission, so readily observed in the spirem of the pro- 
phase of the heterotypic mitosis, is not a real longitudinal fission of 
the chromatin thread, but that, during the contracted phase of the 
nucleus, the so-called “‘synapsis,” the double spirem is formed by the 
approximation of two spirems, one being maternal and the other 
paternal. The chromosomes are therefore bivalent, and as they 
separate in metakinesis each splits lengthwise. BERGHS has stu 
Convallaria majalis, Lilium speciosum, Allium fistulosum, Narthecwum 
ossifragum, Helleborus joetidus, and Drosera rotundifolia, 
he has presented an apparently closely connected series in the forma 
tion of the chromosomes, certain very important steps ° Z 
have been omitted and others incorrectly interpreted. 
STRASBURGER (04) has based his conclusions upon 4 study e 
| favorable 
Galtonia candicans, a species claimed to be unusually 
because of the small number of the chromosomes in re gre 
mother cells, namely six. In this plant he finds that the ess as 
longitudinally in the early prophase of the heterotypic MNOS? 
described by the writer several years ago, but the longitualn “8 
ting does not lead to the separation of the segments; 5° 
the spirem shortens and becomes thicker, no trace of this 
be seen. The spirem now segments transversely ; 
mosomes, and each of these segments again, in a similar mann” 
into the six seit 
! 
