Halophytes have evolved characteristics to adjust to the stressful conditions in their native habitats by means of a number of different adaptive responses at the germination stage of development. The level of expression of salt tolerance by plants at the germination stage cannot always be correlated with tolerance at later stages of development. The interaction between thermoperiod and salinity was investigated for the succulent-perennial desert shrub Zygophyllum qatarense. The development of somatic seed polymorphism is of selective advantage to plants, because it permits plants to respond directly to changing environmental conditions by directing their reproductive allocation into different seed morphs. Josselyn and Perez determined that seeds of S. marina also made up a considerable portion of the seed bank on a California coastal salt marsh. Many highly salt-tolerant species do not germinate at seawater levels of salinity and that increases in salinity inhibit their rate of germination, delay the start of germination, and cause a decrease in total germination.