310 University of California Publications in Botany [Vol. 5 



and sylvestris. No good pollen is produced and thus one would expect 

 the flowers to fall just as in all these other partially sterile hybrids. 

 Contrary to this expectation, many of the flowers on F^HITG are 

 retained finally to mature fruits of normal size containing masses 

 of small-sized, functionless seed of a type which has been called 

 "phenospermic." This retention of the fruits is shown in the photo- 

 graph (plate 42, figure 1) which was taken at the end of the growing 

 season to illustrate this point. In this connection it must be noted 

 that, just as the calycine-flower character of calycina is recessive in 

 varietal crosses and dominant in crosses with sylvestris, so this 

 partheuocarpic tendency of "Cuba" appears to be recessive in a 

 varietal cross. "Cuba" crossed with "Maryland" gave an inter- 

 mediate Fj in general appearance — self-fertile, of course — but follow- 

 ing a very considerable number of castrations of the F^ flowers only 

 a very few fruits matured. 



This hybrid, in addition to exhibiting the partheuocarpic tendency 

 of "Cuba," bears out with regard to other characters also the general 

 contention that the Tahacum reaction system is dominant throughout. 

 In the case of both parent and hybrid the flower is a greenish to 

 creamy white and the almost pentagonal corolla limb and slender tube 

 with slightly SM^ollen infundibulum of "Cuba" is reproduced in the 

 F^ flower. Leaf characters of hybrid and parent exhibit an equivalent 

 correspondence, though the two photographs on plate 42 do not 

 bring out this point satisfactorily since the parent individual is just 

 coming into flower, whereas the Fj is long past the height of its grow- 

 ing season. The photographs, however, leave no room for doubt as to 

 the general similarity in leaf characters. 



Of the various Tahacum varieties concerned in these hybrids 

 "Cuba" is the most vigorous and possesses by far the tallest habit. 

 The Fi as grown was no taller and indeed did not seem to be quite 

 as luxuriant vegetatively as "Cuba," a situation brought out in the 

 two photographs on plate 42. This fact was probably due to a crowd- 

 ing of the hybrid rows in the field, since they were so close together 

 that the lower leaves were in almost complete shade after the first 

 few weeks of the growing season. This latter fact accounts, also, for 

 the few laterals produced on the hybrid from the central and basal 

 leaf axils as compared with "Cuba" and other more or less superficial 

 differences in habit. We have chosen to discuss this ' ' Cubsi" -sylvestris 

 hybrid even in the absence of as complete illustrative material as has 

 been included in the case of the other hybrids mentioned, primarily 



