205 



The Present Status of the Chromosome Controversy. 



By D. M. Mottiek. 



(Abstract.) 



Cytologists are now agreed that the first mitosis in the spore mother- 

 cells of higher plants is a "reducing" or qualitative division, the chromo- 

 somes being bivalent, and that the second mitosis is equational. Two 

 views, however, are held concerning the manner in which the bivalent 

 chromosomes are formed. Gregoire and his associates; Allen, and Stras- 

 burger and his students, maintain that the double chromatin thread ap- 

 pearing after synapsis is not the result of a longitudinal splitting of a 

 single spirem, but the approximation of two spirems, one presumably 

 paternal and the other maternal. On the other hand, Farmer and Moore 

 and others, among whom is the writer, assert that the double spirem is 

 due to a longitudinal splitting, which, as the spirem shortens and thickens, 

 becomes indistinguishable except in certain cases. Parallel portions of the 

 spirem, or a part of the same, now approximate, forming loops, the paral- 

 lel sides of which are twisted upon each other. This looping or approxima- 

 tion of parallel portions of the spirem is accompanied by a second contrac- 

 tion resembling a partial synapsis. The result is that near the center of 

 the nucleus there is formed a closely entangled or balled up mass of the 

 spirem from which extend somewhat radially the loops or approximated 

 parts of the spirem having a straighter course. Each parallel part of a 

 loop is, for example, a chromosome, the two forming a bivalent chromo- 

 some. The spirem now segments transversely, and in case the parallel 

 sides of the loops or the otherwise approximated parts of the spirem ad- 

 here at one end, as is A r ery frequently true, the spirem may be said to 

 segment into pieces equal to the length of two chromosomes. These two 

 chromosomes, each of which is split lengthwise, now come to lie side by 

 side, or to form rings, loops, X's, Y's, etc. (Lilium, Podophyllum.) The 

 longitudinal splitting of the daughter segments observed during the 

 meta, or anaphase, is, according to this view, the original longitudinal 

 fission of the early prophase. 



