levine: somatic and reduction divisions in drosera 141 



In the cross and median sections of the pollen grains studied 

 I have been able to make further studies on the chromosome 

 number in the nuclear divisions here. Nuclear divisions in the 

 pollen grains of Drosera obovata have been described and figured 

 by Rosenberg ('09) and my observations in general are in perfect 

 accord with his. The pollen grain nucleus divides and two 

 smaller cells are formed, as shown in Fig. 41. I have studied 

 these divisions very carefully in Drosera longijolia and find that 

 the first division of the nucleus results in two equal nuclei. One 

 of these divides again and two smaller nuclei are formed. Cell 

 division follows and the daughter cells lie embedded in the 

 cytoplasm of the pollen grain. While I have not been able 

 to count the chromosomes on the spindle in these divisions, the 

 nuclei of these small cells show prochromosomes. So far I have 

 been unable to count twenty prochromosomes as maintained by 

 Rosenberg for this species. In view of these observations it is 

 quite apparent, as observed above, that further work must be 

 done on this interesting species. It is hoped that cultivated 

 material now growing in our greenhouses as well as fresh field 

 material will be available during the coming summer, so that 

 the reduction divisions in the pollen mother-cells of Drosera longi- 

 jolia can be studied and the two species, D. longijolia and D, 

 rotundijolia, can be crossed in an effort to obtain the so-called 

 wild hybrid D. obovata. 



I wish to mention here my indebtedness to Professor John 

 Davidson for supplying me with material of Drosera longijolia 

 and for his kind interest in the progress of my work. I also wish 

 to thank Professor N. Wille for sending me his herbarium speci- 

 mens of the Norwegian Drosera longijolia and D. intermedia. 

 To Professor R. A. Harper I wish to extend my sincerest thanks 

 for his kindly criticisms and helpful suggestions. 



Summary 



1. The somatic cell division is brought about by the formation 

 of a cell plate similar to that described by Strasburger, Went, 

 and Timberlake for Monocotyledons and Gymnosperms. 



2. The chromosomes of the last premeiotic division form the 

 prochromosomes of the pollen mother-cells, of which there are 

 ten pairs distributed over the linin network on the periphery of 



