Culm Morphology and Development in Winter Wheat

1. Culm measurements were made at 2-day intervals on winter wheat on representative plants of varieties Blue Jacket, Pawnee, and Seu Seun 27 during the entire period of culm development. Blue Jacket, the tallest variety, was also the latest maturing, while Seu Seun 27 was the shortest and the earliest maturing variety. Pawnee was intermediate in both height and maturity. 2. These varieties developed five internodes above the soil surface. 3. Successively higher internodes developed later and grew longer. The increment of length of the successive internodes determined the mature height of the varieties. 4. Differences in the length of corresponding internodes of Blue Jacket, Pawnee, and Seu Seun 27 became greater in the successively higher and longer internodes of the culms. 5. Simultaneous elongation of as many as three internodes occurred in each of the varieties. Elongation of each internode began slowly, built up to a maximum, then decreased. The data indicated that elongation of an internode began at approximately the same time that the rate of elongation of the internode immediately below began to decrease, an exception being the peduncle, which began elongation at about the same time as the fourth internode but which continued to elongate well after elongation of the fourth internode had ceased. 6. Major elongation of the spike occurred concurrently with the elongation of the third internode in all three varieties.