Question
How does a seed plant survive if rain falls only during one short season each year and water is deep below the soil surface?

Answer
Michele,

Seeds are one of the beautiful aspects of evolution.  

Inside of each seed there is a living embryo consisting of a root and leaves.  As a seed matures at the end of the season it drys and enters a state called quiesence.  A quiesent seed is capable of germination when conditions are suitable.  Typically most seeds form in late summer to fall and would germinate except for the cooling weather and wait until spring and warming temperatures and rainfall.  

I hope this helps

Gary