462 University of California Publications in Botany [Vol. 5 



macrophylla series, from alha and macrophylla. In the course of the 

 investigations other crosses were made between different varieties of 

 Tabacum and to a limited extent between other species of Nicotiana; 

 but the principal attention has been paid to the three crosses noted 

 above, and they and their progenies alone will be considered in the 

 present paper. It may be said at this point that the different varieties 

 of Tabacum cross readily with one another, giving an abundance of 

 good viable seed. The hybrids are uniformly self-fertile. 



The methods of hybridization used need not be considered here, 

 because they have been described in detail by Goodspeed (1912) else- 

 where in this series. The particular refinements of technique which 

 must be employed in sowing the seed, on account of its very small size, 

 have also been there described. It might be well to state, however, 

 that the most refined methods doubtless will not prevent the occasional 

 appearance of a stray plant in the cultures. The danger of contami- 

 nation arises not only during the sowing of the seed, but also when the 

 bags are placed over the unopened buds. It is very easy to include a 

 few stray seeds under the bag, for their small size makes it almost 

 impossible to detect them in the coarse, sticky indumentum of the 

 plant. In spite of these obvious difficulties, however, the number of 

 plants that have certainly been strays has been very small. Their 

 rare occurrence indicates clearly that the technique employed has been 

 very successful. 



III. ANGUSTIFOLIA-MACROPHYLLA SERIES 



This series has received the most attention since the parents are 

 so distinctly different, and the results have consequently been more 

 complex than those which have followed the crossing of any other pair 

 of Tabacum varieties. As will be demonstrated below, F, seemed at 

 first hopeless in its variety of segregation. Later generations, however, 

 exhibited so much less, or so little variety in their segregation products 

 that it was easy to obtain new permanent combinations of characters 

 or "fixations." Certain of its segregants have been followed out to 

 F., and have also been crossed back on the parents which they most 

 closely resembled. 



Six successful crosses were made. Of these H^^ and Hg had macro- 

 phylla for the male and angustifolia for the female parent, while H^, 

 Hg, Hi5, and H^g were reciprocal crosses. As a matter of convenience 



