1917] Goodspeed-Clausen : F^ Species Hybrids in Nicotiana 305 



year of growth upon its own roots. It is also out of flower. Its 

 height, as contrasted with that of the hybrid and of angustifolia, is. 

 however, rather characteristic and in general its distinction from 

 angustifolia, and thus from the F^ also, is no more striking than is 

 that of the thorouglily typical plant of sylvestris shown in plate 40, 

 figure 2. Nicotiana (Tahacum) angustifolia is one of the most con- 

 spicuous members of the assemblage of Tahacum forms represented 

 in our cultures. The distinctly petioled leaf is very noticeable, as is 

 the characteristic drooping habit of the leaves. This latter peculiarity 

 is emphasized by the occurrence of narrow, strap-like leaves along 

 the upper third of the laterals, which leaves hang almost straight 

 down from their point of insertion. 



The Fj, as shown in plate 38, represents an expanded expression 

 of the general angustifolia habit. It is to be noted in this connection 

 that the rather marked corymbose habit of angustifolia might not 

 seem to be reproduced in the F^ since the laterals do not overtop and 

 indeed do not equal the height of the terminal inflorescence. This 

 situation may, it seems, be taken to represent merely a resultant of 

 the generally increased vigor of the Fj as compared with either parent, 

 since particular F^ individuals restricted in growth by cultural con- 

 ditions have been seen to exhibit a more nearly corymbose habit. The 

 number of laterals, somewhat greater on the hybrid than on angusti- 

 folia, has in the same fashion shown itself to be a function of the 

 amount of vegetative vigor displayed. 



Parent and hybrid flowers are shown in plate 43. In general the 

 infundibuliform corolla of all the Tahacum varieties and of the Fj 

 species hybrids is in striking contrast to the long, slender-tubed corolla 

 of sylvestris which, though slightly enlarged somewhat above the 

 middle of the tube, narrows again as the tube passes out into the limb. 

 Of all the Tahacum forms here figured, angustifolia is characterized 

 by the most slender corolla tube and the least inflated infiindibuluni, 

 and still its corolla tube characters and those of the F^ hybi"ids set it 

 off sharply from sylvestris. The calyx of sylvestris is also highly 

 characteristic and is in definite contrast to the various modifications 

 of tlie Tahacum calyx seen in its several varieties. Thus, the deeply 

 cleft calyx tube of angustifolia which is clearly apparent though less 

 ample in the F,, is distinctly different from the smaller calyx tube of 

 sylvestris with its short, blunt teeth. Finally the configuration of the 

 corolla limb in sylvestris is distinct from that of any of our Tahacum 

 varieties. In this case, for example, the deeply divided corolla limb. 



