Chromosome counts of stages of meiosis could be made from anthers of some female flowers of P. traversii and, especially in a few flowers of P. “short tussock” and P. “snow tussock”, pollen was noticed during the very early development of female buds in marked plants. By the time buds were ready to open their anthers were shrivelled and pollen was unrecognizable. In one female P. “short tussock” plant with mature flowers, the anthers, indehiscent and shrivelled, contained collapsed pollen. Frankel (1940) found this phenomenon in Hebe townsoni. Some of the meiotic figures in plants at Cass (the sexes of the parent plants were not determined) appeared to show one set of unpaired chromosomes during second metaphase. These may have been females with degeneration setting in. In Pimelea some emasculated hermaphrodite flowers showed slight reduction in size from normal.

It appears possible that corolla growth is influenced by a hormone produced in the anthers and released post-meiotically. Determination of corolla lengths probably occurs at a stage later than that of the determination of sex of the flower. A paper by Plack (1957) deals with a very similar situation in a sexually dimorphic Labiate, Glechoma hederacea. In this normally gynodioecious species she found that some individuals produce female flowers only, others are gynomonoecious, and the proportion of female to hermaphrodite flowers varies with the stock and the season. This parallels the situation in P. traversii at Cass in all respects. Glechoma is four anthered. Flowers intermediate in size between the small females and larger hermaphrodites had one, two or three anthers. Artificial emasculation of hermaphrodites in bud showed that corolla size was reduced. Plack thought that corolla growth is influenced by a hormone produced in the anthers and released after meiosis since the critical time for growth of corolla (or lack of it) was at a certain corolla length. There appears to be a close similarity between Pimelea and Glechoma in these respects.

In a more recent paper (Plack, 1958) it is shown that treatment with Gibberellin caused growth of small female corollas in Glechoma, to the larger hermaphrodite size.

Baker (1948) states that the wide range of dicotyledons in which small female flowers and larger hermaphrodites are found indicates a common factor in their origin, and there is a strong suggestion from the above evidence that hormone balance controls flower size. A considerable body of information is summarized by Heslop Harrison (1957) who wrote of experimental modification of sex expression. It has been shown in certain plants that various factors of environment may affect development of flowers (with consistent experimental results for either monoecious, dioecious or hermaphrodite plants) causing variations in sex expression. These variations are considered to be due to hormonal causes, the environmental factors affecting production or movement of hormones which control sex. Heslop Harrison suggests that, as flowers are initiated at the apices, the auxin levels favouring optimum development of one sex suppress the other. In a normal environment the mechanism of sex inheritance establishes in some individuals one developmental path and in some the other.

Baker (1948) states that “Because functional pistillate flowers may be distributed in a gynodioecious or gynomonoecious manner in the same species, abortion of anthers cannot always be determined by direct genetic means…”. These ideas do not, however, necessarily conflict with the concept of genetically controlled gynodioecy. Most individuals in populations of Pimelea are clearly of one sex or the other and remain so from year to year.