1917] Goodspeed-Clausen : F^ Species Hybrids in Nicotiana 311 



because it illustrates the fact that such an obviously extra-normal 

 characteristic as parthenocarpy when combined in the Tahacum re- 

 action system is manifested in the partially sterile hybrid with 

 sylvestris along with all the other attributes of the reaction system 

 in which it occurs. 



FjH33 — N. sylvestris X N. Tabacum var. macrophylla purpurea 



This hybrid is shown with its Tabacum parent in plate 37. It was 

 made in 1909 by Professor W. A. Setchell, who grew it in 1910 and 

 has turned over to us his notes upon its general appearance. We are 

 greatly indebted to Professor Setchell in this regard and also for his 

 continued interest in and many valuable suggestions concerning the 

 progress of the experiments dealing with the Tabacum-sylvestris 

 hybrids. We introduce FiH33 into this discussion with only brief 

 comment merely as further evidence of the dominance of a reaction 

 system, the factors within which act together in so remarkably unified 

 a manner when in contact with a totally different set of factors which 

 go to make up a totally different reaction system. 



The plants of F^H33 seemed when first grown, and still are, re- 

 markable for their vigor and vegetative luxuriance, although among 

 the species hybrids more recently made other types of the Tabacum 

 reaction system crossed with sylvestris have produced plants of equal 

 size. The photographs in plate 37 emphasize the correspondence 

 between hybrid and parent both in general habit and in particular 

 characters. Particular leaf characters are closely similar to those 

 of the Tabacum parent, but the characteristic, sharply pinched-in leaf- 

 base of macrophylla purpurea, which is recessive in crosses with 

 Tabacum varieties having the broad type of leaf-base, is not faithfully 

 reproduced in the F^ hybrid. Instead, the leaves of the F^ hybrid 

 exhibit a narrow form of the broad type of leaf-base, an expression 

 which is intermediate between the broad type of sylvestris nnd the 

 sharply pinched-in type of macrophylla purpurea. 



Flower color in the Tabacum parent and in the hybrid was a deep 

 red, a somewhat deeper shade of red than that peculiar to the flowers 

 of macrophylla and FjIISS. The flower of macrophylla piirpnrca is 

 strictly of the macrophylla type, but considerably larger, and the F, 

 flowers are identical with the former in shape and in proportion of 

 tube length to spread of limb, tliough of a somcwliat larger size. 



