Seedlings of the arboreal, ground-germinating, tropical vine Monstera gigantea (Engler) are shown to grow directly toward potential host trees; they do not find hosts by haphazard growth or random searching. Our experiments show that these vines are attracted to the darkest sector of the horizon. In nature trees provide these dark sectors. We term this response skototropism (growth toward darkness). Skototropism is probably produced by a modification of the molecular and cellular mechanisms that produce negative phototropism. We introduce the new term to emphasize the adaptive nature of the response; whereas the term "negative phototropism" can imply either growth away from light or growth toward darkness, only growth toward darkness can lead the vine directly to a host. This is because, in nature, hosts will not be aligned 180 degrees from the lightest sector of the horizon relative to the vine.