{^AKI^*^ 



CHROMOSOME NUMBERS IN THE GENUS HYPERICUM 379 



chromosomes, but l)et\veeii 20 and 30 chromocenters. Conseqiiently, 

 the chromocenters are hardly prochromosomes, as far as Hypericiim 

 is concerned. According to Lundegårdh's (1913) grouping of the 

 piants by the behaviour of chromocenters, Hypericum belongs to the 

 Vicia type, which lias a varying number of chromocenters. 



THE REDUCTION DIVISION. 



The first phases of the reduction division have not been investiga- 

 ted to such an extent as to make it possible to account for the course 

 of the prophasis. The diakinesis contains gemini in a number cor- 

 responding, to that of the chromosomes. The gemini are of different 

 shape; generally the chromosomes are parallel, but also other forms are 

 found (V, ( ), X). Towards the diakinesis the nucleolus becomes less 

 stainable, and, ultimately, it disappears completely; it retains its glo- 

 bular shape until the very last. The chromosomes are arranged in one 

 plane, and the membrane of the nucleus is dissolved. The spindle, 

 in the equatorial plane of wbich the chromosomes are arranged, is 

 distinctly visible and has the ordinary shape. The twinned chromo- 

 somes part and wander to their respective poles; the separation takes 

 CM 'place simultaneously, and no irregularities, remaining or discharged 

 "— chromosomes, etc. are seen. In the metaphasis no separation of the 

 ^^ chromosomes for the homoeotypical division can be detected; in the 

 anaphasis such division is distinctly visible. After the chromosomes 

 have reached the poles, a splitting of the individual chromosomes is 

 distinctly seen. The appearance of the chromosomes changes, the 

 outlines become indistinct, the chromosomes are connected by fibres, 

 and the \Vhole object gets a vacuolated appearance. The nucleus is 

 surrounded by a membrane. No wall is formed between the daughter 

 nuclei, but in a plane at right angle to the center of the connecting line 

 between the two nuclei a dense plasm develops, which remains there 

 until the homoeotypical metaphasis. 



At the time when the homoeotypical division shall take place the 

 regenerated chromosomes are arranged in a plane at right angle to the 

 spindle, and a chromosome from each pair wanders to the pole. Nor 

 this division shows any irregularities. The chromosomes are consi- 

 derably smaller than at the time of the heterotypical division, and, 

 consequently, it is far more difficult to study the details. In the 

 telophasis the chromosomes assemble and become alveolated. A mem- 

 brane around the nucleus is formed, and 1—3 nucleoles appear. The 





