368 THE WHEAT PLANT 



The gametic constitution of fully-bearded plants would be represented 

 by BBTT, the short-tipped plant by bbTT, and the strictly beardless by 

 bbtt. 



Crossing a fully-bearded (BBTT) with a beardless plant (bbtt) would 

 give an F l of the constitution BbTt, which in F 2 would produce : 



i BBTT (fully bearded) +4 BbTt (very short tips) +2 BbTT (nearly 

 bearded) +2 BBTt (half bearded) + 1 bbTT (short tips) +2 bbTt (minute 

 tips) + 1 BBtt (long tips) + 2 Bbtt (very short tips) + 1 bbtt (quite beard- 

 less). 



The fully-bearded, quite-beardless, " long-tipped," and " short- 

 tipped " plants of the F 2 generation just mentioned bred true in F 3 ; 

 later the two latter were proved to contain the respective constituent 

 factors which on combination gave rise to the fully-bearded character. 



These results, although probably of limited application, are of much 

 interest and help to explain the existence of semi-bearded " long-tipped " 

 forms (BBtt), which breed true, as well as the production of fully-bearded 

 wheats from the crossing of forms which would ordinarily be classed as 

 " beardless " (see below). 



A repetition and extension of the work of crossing bearded and the 

 various " beardless " forms with accurate measurement of the awn 

 lengths of the descendants and mathematical analysis of the results is much 

 to be desired. 



Tschermak states that in the two hybrids Fiirst Hatzfeldt (beard- 

 less) x Galician (bearded) and Mold's white (beardless) x Hungarian 

 (bearded) the bearded character was lost and did not appear among the 

 descendants. 



iii. Beardless x Beardless. In almost all cases the crossing of two 

 " beardless " forms results in " beardless " offspring both in the F x and 

 all subsequent generations. 



Rimpau, however, observed a small number of constant bearded plants 

 among the progeny of the second generation of a cross between two 

 beardless wheats, Saxon " Land " wheat and Squarehead, and Spillman 

 obtained bearded forms from the cross Little Club x Farquhar, both 

 beardless parents. 



The Howards also record the production of fully-bearded plants in 

 F 2 from the crossing of " long-tipped " and " short-tipped " " beardless " 

 wheats. Assuming the gametic constitution of the parents to be BBtt 

 and bbTT respectively, the Fj would be represented by BbTt, and, as 

 explained above, some of the descendants of this hybrid would be fully 

 bearded in the F 2 generation. 



It is, however, improbable that this explanation covers all cases of the 

 appearance of fully-bearded plants among the progeny of crosses of 

 " beardless " wheats. 



