You are speaking about a very important symbol from Chapter 3 of Anderson's young adult novel called Chains. The seeds are important to Isabel because they are not only a reminder of her family but also a symbol of possibility of both growth and freedom.
Isabel longs for her previous life with her family. Isabel, of course, is a slave. She was promised her freedom by her former master's mistress, but when that mistress died, there was no proof. As a result of this unfortunate circumstance, Isabel is promptly sold to Mr. Lockton who is both rough and abusive. As Isabel is forced to leave her home, she is only allowed to take blankets and shoes. She is not allowed to take anything important to the family, such as Ruth's special doll or the carved wood bowl that Poppa previously made them. Isabel is desperate for a reminder of her family, so she takes a few flower seeds that can be easily hidden. These will be the only souvenir she is able to take with her.
In conclusion, it is important to note that these seeds become a prominent symbol in the novel: a symbol of growth and freedom. Isabel hopes that, one day, these seeds will grow. They are dry and stagnant right now (as she is in a state of slavery), but eventually she hopes to plant them where they can flourish, just as she hopes her whole family will do when (and if) freedom is granted to them.