--Walton C. Galinat

While my phytomer concept (Galinat, Bot. Mus. Leafl. Harvard Univ. 19:1-32, 1959) made it very clear as to the vegetative and floral homologies, examples of genetic recognition of these have been slow to accumulate. The first clue came from phase reversal in which male spikelets metamorphosed into tassel plantlets (Galinat and Naylor, Amer. J. Bot. 38:38-47, 1951).

Then the evidence for overlapping phases came from the phenotype of the mutants corngrass and teopod (Galinat, MNL 40:102-103, 1966). The evidence from a class of defective phase change genes (Bif: barren inflorescence, Neuffer; isp: interrupted spikelets, Sprague; H99: reduced tip, Cowen) indicates that the vegetative phase shuts down by independent gene action from the turning on of the floral phase genes. Normally the turning off of the vegetative phase is synchronized with the turning on of the floral phase. The symbol is that I used previously (MNL 62) to designate interrupted spikelets is not available in that I had also used it to refer to cupulate interspace (MNL 45:98).

While the ligule is not the only part of the leaf component of the phytomer, it is significant that the Vg gene reduces both ligule development during the vegetative phase and glume wing development during the floral phase and, thereby, demonstrating the interphase homologies of these two structures. In general, the effects of the Vg gene are stronger during the floral phase than in the vegetative phase. In the former, it also reduces the sheath part of the leaf (glume), the other floral bracts (lemma and palea) and the rachilla. In the latter it has no obvious effects other than on the ligule.

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