Direction of uppermost leaf whorling determined by chance

Like the mirror-image reversal in pattern of successive phytomers along an axis in maize, the direction of whorling by successive leaves also alternates in opposite directions along the axis. This antidromy sequence was observed previously by Weatherwax (1948) in sectioned embryos of corn. He found that the direction of overlapping by the first leaf is determined solely by chance and is not correlated with position within a pair of spikelets. It should, therefore, be expected that the whorl of the last leaf might also be noninherited.

Because corn is so super-sensitive to light intensity and because the sun's rays in the northern hemisphere appear to move clockwise from east to south to west as the earth spins from west to east, it seemed possible that corn now adapted to the northern hemisphere might have evolved a counter clockwise (left-over-right or male) whorl for its upper leaf. This would allow the uppermost leaf to benefit from having the sun rays penetrate more deeply onto its young actively growing tissue that requires extra energy. But as interesting as the hypothesis seemed, no correlation was found in 212 plants from 22 varieties of Northern Flint now adapted to northern United States and Southern Canada (Table 1). The upper leaf whorling on tillers sometimes differed from that on the main stalk of the same plant. The only correlation that could be found was with a few 10-rowed ears in which row-twisting was in the same direction as the whorling of the uppermost husk leaf. Adequate material adapted to the southern hemisphere was not available for testing.

Table 1.

Walton C. Galinat

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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