- In populations of Tulipa systola Stapf. in the Negev Desert of Israel the number of plants appearing above ground during winter fluctuates from year to year. Between 10 and 70% of adult plants and between 40 and 80% of juveniles do not emerge in permanent quadrats in any year. Most of them reappear the following year. There is a significant positive correlation between the proportion of emergents in T. systola populations and the local amount of rainfall until 1 February. Rain after this does not affect emergence. Non-emergence during 1 year reduces the chance of emerging during the following year. In indoor experiments below-ground shoot and root development was initiated at the beginning of winter in response to the drop in soil temperature, regardless of soil moisture. However, further root growth depended on soil moisture. Early shoot development was independent of root development, but full root development was necessary for extension of the shoot to emerge above the soil.