In Gary Schmidt's novel The Wednesday Wars, why does Mrs. Baker say "Chrysanthemum" to Holling?

In Gary D. Schmidt’s novel for young readers titled
The Wednesday Wars, the word “chrysanthemum” occurs at two crucial
moments.  Early in the novel, Holling Hoodhood good-naturedly offers his teacher, Mrs.
Baker, some advice (which she generally welcomes) about how to be an even more effective
teacher. He suggests that when a student does something well, she should let the student
know by using some kind of secret code. She asks him what specific code she should use.
He replies,

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“Well, maybe ‘Azalea’ for something good, and
‘Chrysanthemum’ for something really
good.’”

In response, Mrs.
Baker thanks Holling for this advice but says that she will simply say in plain English
when someone has done something well.

Later in the book,
after Holling stands up to his domineering father and expresses his own honest opinion
about how life should be lived, Holling feels somewhat
isolated.

After a discussion in which Mrs. Baker implies
that Holling will ultimately live a good and satisfying life, he wishes her
well.

And she
smiled – not a teacher smile. “Chrysanthemum,” she
said.

In other words, Mrs.
Baker uses the code that Holling had long ago suggested in order to communicate her
approval of – and admiration for – his recent
behavior.

This moment is significant for several reasons,
including the following:

• Mrs. Baker’s reply
  suggests that she had paid careful attention to Holling earlier and had perhaps been
  gently amused by his suggested code, even though she had not used it at
  first.


• Her reply suggests that she never forgot that
  earlier conversation, even though she had seemed at the time to dismiss his
  suggestion.


• Her reply suggests the special bond that has
  now developed between this teacher and this student.


• Her
  reply suggests that she wants to communicate her approval to Holling in a way that he
  will especially appreciate and perhaps without her being too
  sentimental.


• Her reply suggests that she realizes that
  Holling will realize the special nature of her communication.  This
  is an exchange that only he will understand.