No. 464.] STUDIES ON PLANT CELL.— VII. 557 



(or parthenogenetically if the antipodal be considered the homo- 

 logue of an e.gg) in Alchemilla sericata (Murbeck, : 02). A sum- 

 mary of the various types of vegetative apogamy, parthenogen- 

 esis, and sporophytic (nucellar) budding, supplementing a list of 

 Ernst (: 01) is given by Coulter and Chamberlain (:03, p. 221). 



We will now take up the few investigations which consider 

 the cytological details of parthenogenesis. That of Williams 

 (: 04b) on Dictyota is the only one treating of a lower type. It 

 seems probable that parthenogenesis in Dictyota is in no sense 

 normal and would not lead to mature plants, since the germina- 

 tion of unfertilized eggs in the cultures of Williams presented 

 many irregularities. The spindles instead of being formed from 

 asters with centrosomes are intranuclear in origin, multipolar, 

 and very irregular in their form. As a result the 16 chromo- 

 somes become scattered and a cluster of daughter nuclei is 

 formed containing varying numbers of chromosomes, sometimes 

 one and sometimes several. It is clear in Dictyota that the fer- 

 tilization of the egg results in the development of an aster with 

 a centrosome which exerts a directive influence in mitosis pre- 

 venting a scattering of the 32 chromosomes and conducting the 

 mitosis in a normal fashion. Williams does not believe that the 

 centrosome is introduced as an organized structure into the egg 

 by the sperm but that it is formed de novo as a result of the 

 increased metabolic activities present in the fusion nucleus as 

 compared with that of the unfertilized egg. 



There have been several important studies on parthenogenesis 

 in the spermatophytes. Some of these papers while establishing 

 the facts of parthenogenesis in various forms, give no details of 

 nuclear history or behavior of the chromosomes. But the studies 

 of Juel (: 00), Overton (: 04), and Strasburger (: 04), present some 

 very interesting data on the cytological features of parthenogen- 

 esis in Antennaria alpina, Thalictrum purpurascens , and several 

 species of Alchemilla. 



Several recent papers indicate that parthenogenesis may prove 

 to be general in certain genera or even characteristic of large 

 groups and therefore a far more widespread phenomenon than 

 has been supposed. Raunkiaer (:03) (abstract in English in 

 Bot. Centralb., vol. 93, p. 81, 1903) proved by cutting off the 



