HYBRIDISATION AND WHEAT HYBRIDS 405 



CLjL 2 compaction, and that the " Squareheads," Bore and Pudel, are of 

 the constitution cl^, neither the factors C nor L x or L 2 being present in 

 these wheats. 



In the crossing of T. compaction CLjL 2 with T. vulgare, where the 

 vulgar e parent is of the long lax-eared form cLjLg, the compactum is 

 generally dominant but not completely so, the F x often resembling the 

 Squarehead " wheats. In F 2 segregation occurs into long-eared plants, 

 intermediate and compactums in the ratio i : 2 : i, but exact measurements 

 of the internodal lengths of the rachis are often necessary to establish the 

 ratios. The heterozygotes, though found to be somewhat less dense than 

 the homozygous compactums, form with them a group sharply differ- 

 entiated from the long lax-eared plants. 



New combinations of the factors in the cross between a compactum of 

 the constitution Cljlg and a lax-eared " Landwheat " cL x L 2 would result 

 in the production of " Squareheads " (cl^) in F 2 : these were found by 

 Nilsson-Ehle, though their number was not so large as the expected i in 3. 

 The " Squareheads " of Rimpau's hybrids may have arisen in this way. 



In crosses between T. compactum and the denser-eared vulgares or 

 Squareheads, the F x very closely resembles the compactum parent. Segre- 

 gation in F 2 is complex and apparently impure, long lax-eared forms 

 longer than the Squareheads, and compactums denser than the Binkel 

 appearing with forms resembling the two grandparental wheats. 



The cross between the Binkel compactum and Bore " Squarehead " 

 may be represented thus : 



CL X L 2 (Binkel) x cl^ (Squarehead). 



From the hybrid 1 four forms would appear in F 2 , viz. : Cl^ (very 

 dense compactum), CLjL 2 (Binkel), cl^ (Squarehead), cLjL^ (long lax- 

 eared forms) ; the first and last being new hereditary types respectively 

 denser and laxer than the compactum and Squarehead grandparents. 



As previously noted, all these were obtained by Nilsson-Ehle, and the 

 appearance of the very dense and very lax ears in some of Spillman's com- 

 pactum x vulgare hybrids may be explained in a similar manner. 



The C factor acts more strongly in shortening the ear internodes of 

 the long-eared wheats than those of the Squarehead form, and the com- 

 pactums CL 1 L 2 , CL]1 2 , CljL.2, Cl^ form a graduated group less homo- 

 geneous than the non-compactums (Squareheads \j\ 2 and " Landwheats " 

 L X L 2 ) of the same cross. 



8. HYBRIDS OF T. sphaerococcum WITH OTHER WHEATS. T. sphaero- 

 coccum x T. dicoccum (see p. 392). 



9. HYBRIDS OF T. Spelta WITH OTHER WHEATS. T. Spelta x 

 T. vulgare (see p. 400). 



