y 



Karyokinesis in Magnolia and Liriodendron witli 

 special reference to the behavior of the chromosomes. 



By 



Frank Marion Andrews. 



. tt I 



With 1 plate. 



So many views and contradictoiy Statements concerning the 

 behavior of the chromosomes during karyokinesis in pollen — mother — 

 cells have been advanced, that it seems desirable to state rather 

 briefiy the more important ones before beginning any discussion 

 of the subject. 



Strasburger 's view — which is now generally accepted by 

 botanists is — that the reduction takes place while the pollen and 

 embryo-sac mother-cells are in the resting stage — and that this 

 reduced number is maintained until the sexaal nuclei fuse which 

 re-establishes the original number of chromosomes. There is, 

 therefore accompanying both nuclear divisions in pollen and spore- 

 mother-cells a longitudinal Splitting of the chromosomes and no 

 transverse divisions. 



Strasburger ^) and Mottier find conclusive proof of this 

 fact in the mother-cells of the pollen and embryo-sac in Lilium. In 

 the Embryo-sac of Lilium martagon where the behavior of the chro- 

 matin was followed with the greatest clearness and certainty the 

 longitudinal Splitting of the chromatin thread which forms a uni- 

 form spirem in each division, can be seen before segmentation 

 into chromosomes — <a fact which leaves no doubt as to the 

 nature of the latter when arranged in the nuclear plate. In his 

 more recent works, however, Strasburger argues that during 

 the first mitosis in the spore mother cells of pteridophtes and 

 spermaphytes a second longitudinal Splitting of the chromosomes 

 takes place during the meta-or anaphase as a preparation for the 

 second mitosis and that consequently no longitudinal Splitting occurs 

 during this division. 



') Strasbur^er and Mottier: Berichte d. Deutsch, bot. Gesellsch. 

 15. 327—332. 1897. 



