What are some symbols in The Good Earth?

In The Good Earth, Pearl S. Buck uses
several examples of symbolism.  The pearls that O-lan places between her breasts, the
House of Hwang, and Wang Lung's disabled daughter (the "fool") are all examples of
symbols found in this novel; of course, there are many
more.

When Wang Lung discovers that O-lan has stolen jewels
from the rich man's house in the city, he is adament that the jewels be "put into land
this very day."  However, it saddens O-lan to part with the precious gems, so Wang Lung
feels compassion for her and allows her to keep two
pearls.

Then
Wang Lung, without comprehending it, looked for an instant into the heart of this dull
and faithful creature, who had labored all her life at some task at which she won no
reward and who in the great house had seen others wearing jewels which she never even
felt in her hand once.

Later
in the story, Wang Lung ceases to truly care for his wife and eventually takes the
pearls, which she has treasured, from her.  The pearls are a symbol for their
relationship; Wang Lung gives a part of himself to his wife, but eventually takes
himself from her (loves others and doesn't care for her).  O-lan treasures the pearls,
just as she treasured her husband.  In both cases, she is powerless against her
loss.

The House of Hwang represents temptation and evil. 
As Wang Lung attempts to obtain for himself all of the luxuries he associates with the
House of Hwang, his life becomes filled with material possessions and he loses sight of
its true meaning.  Wang Lung turns away things he should value most, such as O-lan; as
he grows old, however, he realizes that the temptations of the "Great House" were
valueless.

Wang Lung's mentally disabled daughter, the
"fool," is a symbol of happiness.  She wants nothing except what she must have to
survive, yet she is truly happy.  The child is content with a full belly and a patch of
sunshine in which to rest and warm herself.  Her contentment with simplicity stands in
sharp contrast to Wang Lung's attempts to procure material
wealth.