149 — 



Sutton (28) and Montgomery (110), who have first more inti- 

 mately investigated this phenomenon. 



The following division stages correspond with for instance 

 those of Tanacetum or Taraxacum, and the development of the 

 pollen cells does not offer anything extraordinary. 



The development of the Embryo sac. The reduc- 

 tion process at the development of the ES proceeds altogether 

 in about the same manner as in the case of the PMC. 

 Fig. 'J shows dia- 

 kinesis with distinct- 

 ly different chromo- 

 somes. In fig. 10 a 

 spindle figure is 

 shown with 9 chro- 

 mosomes having the 

 same characteristic 

 shapes as in the 

 PMC. Thereupon 

 the second division 

 takes place and the 

 construction of the 

 tetrad. The lower 

 of these cells be- 

 comes the ES. 



The further de- 

 velopment of the ES 

 takes place in the 

 ordinary way. I 

 have, it is true, not 

 yet succeeded in fin- 

 ding out the fusion 

 of the male and fe- 

 male nuclei, but a calculation of the number of the chromosomes 

 in the eggcell and in the first divisions of the endosperm nuclei 

 shows without doubt that a double fertilization takes place. In 

 the endosperm the nuclei divisions occur at least at the beginning 

 very regularly. Very often I have been able to determine their 

 number at 27, that is to say 9-J-9 + 9. The endosperm nucleus 

 has 18 chromosomes, as it is formed by the fusion of two polar 

 nuclei, each one with 9 chromosomes. 



Fit 



£ 

 II. 



F 



H. venosum, A~ E, heterotypic spindle figures 



in E a polar view; F, anaphasis. 



