FIFTEEN- AND SIXTEEN-CHROMOSOME OENOTHERA MUTANTS 67 
in the majority of cases, from left to right (viewed from the sepal side) 
with the right lateral margin free and the left overlapped by the right 
lateral of the preceding petal (Fig. 4) . Occasionally, when a bud opens, 
it is found that the relative positions of the right and left margins of two 
neighboring petals are reversed, the left of one overlapping the right 
of the other. A few buds have been found in which a complete re- 
3 - 
Fig. 5. Fi 0. Lamarckiana X 0. gigas, plant No. 3750, C.S.H., 1908. Flower 
showing reversed petal arrangement at two points, the left lateral margin of petal 
I (/. m.) overlapping the right lateral of 4 {r. m.) and the left of 3 overlapping the 
right of 2, leaving petals 2 and 4 in, and i and 3, out. 
versal of relative positions had occurred at all four points; commonly 
this takes place at but one. Complete reversal produces no disturb- 
ance, but partial reversal frequently, though by no means invariably, 
causes interference in the growing bud. For example, when the left 
lateral margin of a petal, which we may designate as 2, becomes dis- 
