Abstract: Campanula americana is a self-compatible, protandrous herb which frequently has both gender phases present on the same plant. However, despite opportunities for within-plant pollen movement and the ability of self pollen to produce a full seed set, selfing in natural populations is rare. This suggests the possibility of cryptic self-incompatibility, which would reduce inbreeding when outcross pollen is available, yet ensure reproduction when only self pollen is available. I explored cryptic self-incompatibility in C. americana by first comparing growth rates of pollen tubes of different degrees of relatedness to the pollen-recipient, with the expectation that outcross pollen tubes will grow faster. I approached this hypothesis with two techniques: counting the number of pollen tubes in four sections of the style, and measuring the length of pollen tube clusters. Both techniques revealed no significant differences between self and outcross pollen tube growth rates. However, cryptic self-incompatibility may be present in a form other than pollen tube growth rates, or may only manifest itself only when mixed loads of self and outcross pollen are present on the stigma. In a second experiment, I pollinated maternal plants with different ratios of self and outcross pollen. By genotyping the offspring, I will determine if the proportion of outcrossed progeny reflects the proportion of outcross pollen on the stigma. If cryptic self-incompatibility is present, outcross pollen will sire proportionately more offspring than self pollen.