3 6 4 THE WHEAT PLANT 



HOLLOW AND SOLID STRAW. In the majority of wheats of the vulgare 

 and compactum races, the culms are comparatively wide and hollow with 

 thin walls ; those of T. durum, T. polonicum, and T. turgidum are smaller 

 in diameter and full of pith, or thick- walled with a very small central 



cavity. 



The hollow form is dominant over the solid straw, and F 2 segregation 



is in the 3 : i ratio. 



PUBESCENT AND GLABROUS YOUNG LEAVES. The surfaces of the 

 young leaves of T. durum are nearly or quite glabrous, those of other 

 races being more or less densely clothed with hairs. 



In general the pubescent leaves of T. dicoccum and T. turgidum are 

 dominant over the less hairy and glabrous leaves, but the segregation 

 of the characters in the F 2 generation has not been adequately in- 

 vestigated. 



NORMAL AND BRANCHED EARS. According to Tschermak, the normal 

 condition is dominant over the branched ear of " Mummy " wheat 

 (T. turgidum, var. mirabile) (Fig. 160). 



FRAGILITY AND TOUGHNESS OF THE RACHIS. In the two wild wheats 

 T. aegilopoides and T. dicoccoides the rachis of the ripe ear separates 

 transversely at the nodes, each spikelet with an internode of the rachis 

 attached falling to the ground when the ear is slightly shaken. 



In three cultivated wheats, T. monococcum, T. dicoccum, and T. Spelta, 

 the rachis is also fragile, but in a lesser degree. 



In contradistinction to these are the rest of the cultivated wheats in 

 which the rachis is tough and does not become disarticulated even under 

 the rough treatment of thrashing. 



i. Brittle-eared x Brittle-eared. 



ii. Brittle-eared x Tough-eared. The crossing of two brittle - eared 

 wheats gives a constant brittle-eared progeny, and fragility of rachis 

 behaves as a dominant character when a brittle-eared wheat is crossed 

 with a tough-eared form. 



iii. Tough-eared x Tough-eared. Hybrids of varieties belonging to the 

 same tough-eared race usually have constant tough-eared descendants, but 

 where the two plants crossed belong to different tough-eared races, brittle- 

 eared forms sometimes appear in the F 2 and subsequent generations. 



H. Vilmorin observed brittle-eared forms resembling T. Spelta among 

 the F 2 generation of the hybrids, T. vulgare (Ble Seigle) x T. turgidum 

 (Poulard Ble' Buisson), and T. vulgare ? (Chidham d'automne) x T. 

 durum $ (Ismael). 



Love and Craig record the appearance of two plants with fragile ears 

 similar to those of wild T. dicoccoides out of 1 1 3 plants of the F 2 genera- 

 tion of the cross T. vulgare ? (Early Red Chief) x T. durum $ (Marouani). 



