86 BOTANICAL GAZETTE [JANUARY 
the somatic divisions, the conclusion is drawn that this process represents a 
side-by-side conjugation of somatic chromosomes, which are separated at the 
- first maturation division. 
Morrrer and NoTHNAGEL,” after a study of the pollen mother cells of 
Allium cernuum, come to very different conclusions regarding the conjugation 
process. These stand in agreement with the earlier accounts of MOTTIER, 
and may be summarized as follows. Synapsis is a real contraction of the linin 
net with its chromatin granules. The thick spirem which emerges therefrom 
shows only an occasional temporary split in some parts. Nothing is found to 
indicate a union of two spirems in the prophases. During a second contraction 
the spirem is thrown into loops, and cross-segmentation occurs. The bivalent 
chromosomes so formed are regarded as consisting of two somatic chromosomes 
previously arranged end to end in the spirem. The members of each bivalent 
separate at the first division and during anaphase become longitudinally split 
in preparation for the second. At telophase there is formed an interrupted 
spirem, but there is present no chromatin knot such as BONNEVIE has described 
and which Morrter and NotHNaGEL believe to be due to improper fixation. 
The above works recall the earlier researches of BERGHS*” and of GREGOIRE” 
on Allium fistulosum, in which they found the bivalent ERRORS arising 
through a union of two spirems in the p t as BONNE- 
vie later found in Allium Cepa. The feures as by these writers to illustrate 
these critical stages form a much more complete series than those accompany- 
ing the contribution of Mortrer and NorunacEt. It is hardly probable that 
the disagreement between these accounts is due entirely to the fact that differ- 
ent species of Allium were used.—L. W. SHarp. 
Cytology of mutants.—Some of the cytological aspects of the Oenothera 
question are summarized by GaTeEs*® in a discussion of tetraploid mutants. 
O. gigas, a tetraploid form, in all probability arises through the apogamous 
development of an unreduced megaspore mother cell with 28 chromosomes (42); 
such a cell having been seen by GeErts. Triploid mutants seem to be due to 
the union of a diploid with a haploid germ cell (Stomps, Miss Lutz). In some 
plants the mutational changes are not confined to the meiotic divisions, but at 
» Mortier, D. M., and Norunacet, M., The development and behavior of the 
chromosomes in the first or heterotypic mitosis of the pollen mother cells of Al/ium 
cernuum Roth. Bull. Torr. Bot. Club 40:555-565. pls. 23, 24. 1913. 
2t BERGHS, J., La formation des —— Lapsed cael —— la en ile 
végétale. II. Depuis la sporogonie j 
de sec Jistulosum. La Cellule 21: eee ae 
REGOIRE, V., La formation des gemini POON cp dans les végétaux. La 
cake 24:369-420. pls. 2, 1907. 
3 Gates, R. R., Tetraploid mutants and chromosome mechanisms. Biol. 
Centralbl. 33:93-99, 113-150. figs. 7. 1913. 
