264 Variation in Wild IIojj 



have been met with, both in nature and also among the hybrid offspring 

 produced in certain breeding experiments. 



One of us has pointed out (8) that within the species Broinus mollis 

 two "races" exist, morphologically identical but one susceptible, and the 

 other immune, to certain forms of the mildew Erysiphe Grayninis DC. 



Vavilov (9) states that Triticum dicoccum comprises, with respect 

 to E. Graminis, both susceptible and immune races'. 



Biffen (10), commenting on the characters of the hybrid plants raised 

 by crossing " Michigan Bronze " (a wheat susceptible to the rust Puc- 

 cinia glumarum) with " American Club " (immune), says : " The two 

 parents differ from one another in other characters besides the immunity 

 and liability to the attacks of rust, and it may be noted that, as one 

 would expect, individuals similar to the immune parent morphologically 

 but susceptible to rust were found, and also the rust-proof form of the 

 susceptible parent^." 



General Considerations. 



The various characters reviewed above would appear to have varietal 

 significance, for not only do they persist from year to year in the same 

 individual but all the evidence to hand suggests that many — if not all — 

 of the characters mentioned would reappear on propagating the plants 

 vegetatively ^ Thus two plants have been raised by "cuttings" from a 

 $ seedling (OR 38) and one plant from a cf seedling (Z 11); it was found 

 that the plants raised by cuttings were similar to the original plants in 

 time of flowering, colour of bine, glandulation of leaves and J' flowers, 

 " condition," aroma and colour of the " strig " of the hop-cone, and degree 



1 Ou the general question, Vavilov (9), p. 52, remarks: "the physiological individuali- 

 sation of race is very often accompanied by morphological characters which, however, are 

 externally not very conspicuous. In these cases the peculiarity in behaviour towards fungi 

 obliges the observer to pay more attention to this or that previously unsuspected race, and 

 in the end he usually succeeds in finding in it some other confirmatory dilierences." 



■•^ In another case, it was found that no correlation existed between the leaf-characters 

 of the parent varieties of wheat used in "crossing" and susceptibility to rust — "the 

 immunity [in the F2 generation of the hybrids] simply depended on the luck of the shuffle" 

 (Biffen (11)). 



^ This has been shown ((2), p. 177), by systematic records to be the case with the 

 corresponding characters of (J plants raised from seeds taken from cultivated varieties. It 

 is also to be noted that the characteristic features of certain recognised commercial 

 varieties (which are propagated vegetatively by cuttings) are of the same order as some of 

 the characters discussed in this paper, e.g., early flowering ("Early Bird" variety), pale 

 green bine ("Canterbury Whitebine "), very pleasant aroma (" Goldings "), large size of 

 hop " cone" and strong aroma ("Fuggles"). 



