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The size advantage hypothesis suggests that natural selection will favor size-dependent sex expression when one sex gains more than the other by being large. But members of a minority sex will also have a higher reproductive value, on average. Thus, an individual's reproductive success depends on the reproductive decisions made by neighboring individuals. As a result, the optimal relationship between size and sex may differ among populations. In Arisaema triphyllum, the probability for an individual to be female increases with size, regardless of the character measured. A reciprocal transplant experiment showed the relationship between size and sexual expression is environmentally plastic. Plants originating from our two study sites became female at a larger average size when grown at one site than when grown at the other. In addition to environmental influence on sex expression, the experiment demonstrated genetic differences in the relationship between size and sex. Plants collected from one site became female at a larger size than those from the other, regardless of where they were grown. Thus, while the environment in which an individual was grown had a substantial influence on its sex expression, populations only a few kilometers apart have genetically different relationships between size and sex. Key words: Araceae; Arisaema triphyllum; Connecticut; environmental sex determination; jack-in-the-pulpit; local differentiation; plasticity; reciprocal transplant; sex change.

Plants' programs of development can be considered evolved traits. If this is correct, then we should be able to detect variation among clones in developmental traits and demonstrate that this variation leads to fitness differences. Here we report variation in three developmental traits: timing of shoot emergence and senescence and the timing of shoot type determination. We demonstrate significant variation among colonies for all three traits. A reciprocal transplant experiment in the field goes on to demonstrate that the timing of emergence and senescence has both a genetic and environmental component. Variation in emergence and senescence date should effect clonal resource dynamics while variation in the timing of shoot type determination should effect how both short and long term environmental variation influences the demographic trajectory and, hence, fitness of different clones. Further reciprocal transplant experiments are needed to demonstrate genetic variation in the timing of shoot type determination.

Plant-mycorrhizal interactions are generally considered to be examples of a mutualism in which both plant and mycorrhizal fungi benefit. Plants gain increased access to soil nutrients, particularly phosphorus, while mycorrhizal fungi gain access to the carbon fixed by plants. However, there are exceptions to this pattern. Numerous workers have noted that some plants shed mycorrhizal fungi when soil nutrients are supplemented, suggesting that under nutrient rich conditions, the costs to the plant of maintaining the symbiosis outweigh the benefits. In such systems the symbiosis is facultative. Much less is known about plant-mycorrhizal fungi interactions in woodland as opposed to grassland, prairie or agricultural systems. Here we report the nature and properties of the symbiosis in mayapple, Podophyllum pelatum L. (Berberidaceae), a long-lived perennial of the eastern deciduous forest floor. Our data indicate that the mayapple-fungal interaction is facultative; addition of soil phosphorous reduces the intensity of colonization of mayapple roots by mycorrhizal fungi. Of greater interest, we find that not all roots are equally colonized. Roots at young rhizome nodes contain few if any mycorrhizal fungi. Fungal loads increase to their highest level at two to four year old nodes before dropping again. The pattern of soil phosphate depletion mirrors the pattern of mycorrhizal fungi distribution, with the greatest depletion of soil P observed under the most heavily colonized nodes. Hypotheses relating to the regulation of plant-mycorrhizal fungal interactions will be discussed.