E. S. Salmon 197 



growth. In the cases where the "dwarfness" is most pronounced', the 

 plant remains for the second year and longer extremely stunted, pro- 

 ducing a number of shoots only a few inches high with very small and 

 often curled or distorted leaves. PI. IX, fig. 6 shows such a dwarf, at 

 the end of the second year's growth. Such plants apparently — where no 

 sjDecial care is given to their cultivation — die after a few years. The 

 larger " dwarfs," however, may show a vigorous growth in the third and 

 succeeding years, and may produce a veiy large number of trailing 

 stems (frequently over fifty) which radiate in all directions to a distance 

 of 3 or 4 feet. The most vigorous "dwarfs," however, some of which 

 are now 7 years old, have never produced a single normal climbing 

 stem, nor reached a height (or length) of more than 5 feet, — whereas 

 the stems of all the other normal seedlings of the same " crosses " can 

 climb to 20 feet or so. 



" Dwarfs," like the normal plants, are liable to be attacked, and 

 much injured by "mould" {Sphaerotheca Humuli) and "green fly" 

 (Phorodon Humuli), and to be killed by "eelworm" {Heterodera 

 schachtii). 



The second characteristic of " dwarfs " is their absolute sterility, no 

 flowers or rudiments of sexual organs having been produced in any case. 

 Over 200 " dwarfs," arising from various " crosses," have been kept under 

 observation. " Dwarfs " have occuiTed among the normal seedlings in 

 the majority of the " crosses " I have made ; e.g. in 25 " crosses " in which 

 the following female (English) varieties of hop were used ; — Cobb's 

 Golding, Colgate, Fuggles, Early Bird, Early White, Canterbury White- 

 bine. The male hops used were different individuals of the English 

 forms of the male hop, and in one case a male hop obtained fi'om 

 Oregon, U.S.A., which differs in leaf- and other characters, from the 

 English forms. 



As some of the " dwarfs " are now 7 years old, and as the normal 

 seedling produces flowers in the second year after germination, it appears 

 safe to conclude that the present kind of dwarfness, unlike that recorded 

 in Humulus japonicus by Figdor^, is associated with absolute sterility. 



With regard to the proportion of dwarfs that may occur in the 

 Fi generation, the following facts are available. 



' "Dwarfuess" is most pronounced in those "crosses" in which the male hop is a 

 form from Oregon, U.S.A., and the female a variety cultivated in England. 



2 W. Figdor, Uebergangsbildungen von Pollen- zu Fruehtblattern bei Humulus japoni- 

 cus Sieb. et Zucc. and deren Ursachen, in Sitzuvgsber. d. hniserl. Akad. d. Wissensch. 

 Wien, Bd. cxx. Abt. 1 (1911). 



