574 



THE AMEBIC AX X. I 'IT' It A LIST [Vol. XLIII 



prochromosomes could not be recognized. As the nuclei of these 



come^onnected with one another by delicate threads alonir which 

 the chromatic substance is distributed so that two parallel sys- 

 tems of threads are constructed which finally become so closely 

 associated as to form a single spirem. The chromatin granules 

 of Trollius gather and fuse into larger masses which are at first 

 more numerous than the chromosome count but show a tendency 

 to pair. These are distributed over a delicate linin network 

 upon which the chromatin becomes distributed. Finally the 

 chromatic masses fuse thus forming a single spirem. 



The later history of the reduction processes is similar in all 

 of the types. The spirem splits fstrepsinema stage) and seg- 



become distributed in the nuclear rarity diakinesis ' as pans of 

 chromosomes. The halves of the split segments of the spirem 

 may then be regarded as the sporophytic chromosomes to be 



regarded as of special significance, but merely as an accom- 

 paniment of this period in the development of the bivalent chro- 

 mosomes. The phenomenon of synapsis is regarded as especially 

 significant since it is the period when the sporophytic chromo- 

 somes are in their most intimate relation to one another. 



Rosenberg in two recent papers gives additional evidence in 

 support of his belief (1904) in the permanence of the chromo- 

 somes, and develops further his views on the significance of 

 synaptic phenomena. The first paper 3 deals especially with 

 Hieracium venosum and H. auricula. A brief introduction out- 

 lines clearly the problems concerned with the prochromosome or 

 gamosome theory and their relation to the views on the interpre- 

 tations of the events of synapsis and the reduction divisions. 



The chromatin is present in the resting nuclei of the archespor- 

 ium as irregular deeply-staining masses almost always situated 

 at one side of the nucleus. These are interpreted to be prochro- 

 mosomes or gamosomes, their number corresponding generally 

 to the number of chromosomes which for the sporophyte is four- 

 teen and eighteen in these two species of Hieracium. As the 

 nuclei of the pollen mother-cells approach synapsis the prochro- 



* Rosenberg, O v " Zur Kentniss der prasynaptischen Entwicklungs- 

 phasen der Reduktionsteilung, " Svenik Bot. Tidsl:, I, p. 398, 1907. 



