No. 557] PARTHENOGENESIS IN NICOTIAN A 289 



The Effects of Fobeign Pollen 

 Gartner (Burbidge, 1877), while making species 

 crosses, obtained seed in a few cases which produced 

 plants true to the maternal species and also true hybrids. 

 Mrs. E. H. Thomas (1909) and Professor E. M. East 

 have also observed the same phenomenon in their work. 

 Professor East's results were as follows: 



Seed was obtained which produced plants like the 

 mother species and also true hybrids, from crosses 

 N. paniculata 4 X N. alata var. grandiflora, N. rustica X 

 N. tabacum, and N. tabacum X N. Bigelovii; seed which 

 produced plants like the mother species and no true hy- 

 brids, from crosses N. paniculata X N. Langsdorffii, 

 N. paniculata X N. longiflora, N. paniculata X N. For- 

 getiana, and N. Bigelovii X N. sylvestris; and seed which 

 produced no true hybrids on one occasion but did pro- 

 duce true hybrids on other occasions, from cross N. taba- 

 cum var. lancifolia X N. alata var. grandiflora. These 

 crosses gave per capsule from one to twenty-five good 

 seeds that produced plants true to the mother parent, 

 and many angular and undeveloped seed that produced 

 very few hybrids. In the cases where no hybrids were 

 produced, abortive seeds — probably hybrid in character 

 —were present. 



These seeds, true to the mother species, are thought 

 by Professor East to be due to adventitious embryos 

 arising from the tissue of the nucellus, for no case of 

 seed formation after simple castration occurred in some 

 hundreds of experiments, nor did seed giving maternal 

 plants arise in any but wide species crosses giving sterile 

 or nearly sterile progeny. If such be the case, partheno- 

 genesis did not occur in these crosses. 



Pollen grains of certain species in the plant kingdom 

 are known to be capable of instigating the development 

 of parthenocarpic fruits and of polyembryonic seed of 

 foreign species, but whether they can cause the partheno- 

 genetic development of ovules is still a question; even 



* The authorities for the specific names of the Nicotiana species used in 

 these experiments are given on p. 23. 



