During germination, orthodox seeds loose their ability to tolerate desiccation. We determined whether the critical proportion of a seed's germination time after which desiccation tolerance is lost (CIP) is constant within and between species for nine species of neo-tropical pioneer trees. Seeds were imbibed for various periods before being desiccated. Following desiccation, seeds were re-imbibed and subsequent germination recorded. We found that the CIP was constant within species and was similar for the different species (60–70% of the germination time). Consequently, the maximum number of seeds that can be killed by a single desiccation event, during germination, should increase in seedlots that either have a longer time to germination, or have a narrow range of times to germination. This prediction provides an empirical explanation for the typically observed across species relationship of an increasing spread of germination times within increasing time to 50% germination.