SPECIES CROSSES IN THE GENUS NICOTIANA. 227 



To face p. 226. 



Note added March 22, 1909. 



Since writing the above I have had the opportunity of 

 reading an extremely interesting paper by De Vries (Uber die 

 Zwillings bastarde von CEnothera nanella. Berichte d.d. Bot. 

 Ges. XXVI.a, No. 9). From this it appears that two forms 

 of CEnothera, which originated in a cross, and are distinguished 

 as Laeta and Velutina respectively, possess female gametes, 

 half of which bear the tall and half the dw'arf characters. All 

 the functional pollen grains of Laeta bear the tall character, 

 and all the functional pollen grains of Velutina bear the dwarf 

 character. De Vries does not offer the obvious suggestion that 

 half the total number of pollen grains in each case are impotent. 

 If this suggestion should prove to represent the truth, CEno- 

 thera laeta would afford a case of a hybrid which breeds true 

 in spite of the fact that typical segregation takes place among 

 its germ cells. In the light of these facts it is clear that 

 non-segregation cannot be asserted in any given case, until 

 the hybrid has been crossed with each of the parent forms on 

 a considerable scale. — R. H. L. 



Plate 27. — N. paniculata. Height, 20^ in. 



Plate 28.— N. alata. Height, 28 m. 



Plate 29. — N. tabacum. 



7(1)09 (30) 



