C. S. Lewis received a lot of correspondence from strangers, as you can imagine, and he was very diligent about answering it. I read his Letters to Children yesterday, and on Tumblr posted something he wrote to his godchild about the kinds of things people do.
Below is another passage, this one having to do with language. It was addressed to “Kathy” and was sent in April 1963:
By the way I also wd. say “I got a book”. But your teacher and I are not “English teachers” in the same sense. She has to put across an idea of what the English language ought to be: I’m concerned entirely with what it is and however it came to be what it is. In fact she is a gardener distinguishing “flowers” from “weeds”; I am a botanist and am interested in both as vegetable organisms.
The gardening analogy reminded me of Otto Jespersen’s description of the language as “like an English park . . . in which you are allowed to walk everywhere according to your own fancy”. But this might give a child the wrong idea.
There is much to admire in the metaphor Lewis uses to convey, without prejudice or guile, the difference in attitudes between Kathy’s teacher and himself.
Update:
A post I wrote for Macmillan Dictionary Blog looks at some more examples of the linguistic botany analogy.
Sentence first 
Great analogy. It also reminds of Geoffrey Nunberg’s analogy in “The Decline of Grammar.” He compares prescriptivists to landscape gardeners, but instead of going for the obvious comparison to botanists, he says that it’s like they’re worrying about halting continental drift. I always felt like it was a bad analogy to score a cheap rhetorical point.
What’s lovely about that analogy is that it doesn’t disparage the gardener or the botanist. Nicely done.
Jonathon: I like that essay of Nunberg’s, but I don’t think it’s fair to landscape gardeners! Here’s the passage in question:
Kory: Yes, it’s a generous way to convey the conflict to a child, giving her a noble occupation with which to compare or align herself no matter her sympathies or tendencies: pruning and tidying or observation and taxonomy.
[…] “You can’t weed the world, but you can cultivate your garden” — that echoes an analogy by C. S. Lewis I wrote about recently. […]