i9o8] YAMAXOUCHI—APOGAMY IN NEPHRODIUM 305 



peculiar development of the embryo sac in the parthcnogcnctic 

 Taraxacum officinale. The species produced pollen with a normal 

 reduction of chromosomes, and 13 bivalent chromosomes were present 

 in the heterotypic mitosis; but the megaspore mother cell undergoes 

 a single mitosis and there are formed two daughter cells, the lower one 

 of which develops into the embryo sac. This mitosis passes through 

 the synapsis and leptonema stages as usual, but the heterotypic figure 

 is not organized; it is a typical vegetative one with the univalent 24-26 

 chromosomes. The nuclear divisions in the cmbr3-o sac were not fol- 

 lowed by JuEL, but, accepting the results of Murbeck, he believed that 

 the egg nucleus retained 26 chromosomes — the sporoi)hytc number. 



OvERTOX (53, 54) found a normal reduction in the pollen mother 

 cells of Thalktrum purpurascens and showed tliat the number of 

 chromosomes is 24 for the sporophyte and 12 for the gametophyte. 

 The development of the embryo sac is of two types. In some cases a 

 tetrad is formed from a megaspore mother cell, with all the phenomena 

 of a reduction division; the lowest cell develops into the embryo sac. 

 But many embryo sacs are formed in a different way. The first mitotic 

 figure in the megaspore mother cell is not heterotypic, and shows 24 

 univalent chromosomes; and the same number is counted m the 

 second division in the parthenogenetic embryo. He concludes that the 

 sporophytic number (24) remains unchanged in the embr}'0 sac in this 

 case, and that the egg nucleus with the sporophytic number develo})^ 

 into the embryo parthenogenetically. 



Strasburger (66) made an extensive study of numerous species 

 of AlchemiUa § Eualchemilla, the group which furnished the 

 material for Murbeck's important discoveries. IMost of the forms in 

 Eualchemilla develop normal pollen and a reduction division was 

 found both here and in AlchemiUa arvensis of § Aphaxes. In the 

 heterotypic mitosis in the pollen mother cell, Strasbugrer found 32 

 bivalent chromosomes, which :Murbeck counted as 16. In the embryo 

 sac development in apogamous species the two characteristic divi- 

 sions of sporogenesis are cut out and no tetrad is formed. ^ The nucleus 

 of the megaspore mother cell emerges from synapsis with the sporo- 

 phytic number of univalent chromosomes, and the ensuing division is 

 typically vegetative and not heterotypic. The nuclei of the embrjo 

 sac thus contain the sporophytic number and parthenogenetic develop- 



