What did the professor stress in his book?

W: Professor Johnson, can I talk to you for a minute?
M: Of course, Linda. What can I do for you?
W: Well, I just finished reading your newest book on how to write about the natural world, and I thought it was great.
M: I’m glad you liked it.
W: You know, before I picked up your book, I never thought of nature writing as a specific genre.
M: Not many people do. But really, learning how to describe the natural world is important to all forms of writing. In my book, I stressed that nature writing almost exclusively depends on using your five senses of sight, hearing, smell, touch and taste. The whole purpose of nature writing is to paint a picture of the world around you. If you think about it, creative writing professors teach their students the same things concerning imagery.
W: That may be true, but most of my friends in creative writing class say that one of their big problems is that they don’t use enough description in their works.
M: That’s not surprising. Many writing students have trouble because it’s hard to put the description of the world around them into words.
W: I always had trouble using imagery in my writing until I read your book. After doing some of the exercises you suggested, I feel like my writing has improved some.
M: That’s wonderful. I think if students practiced writing about the natural world, they’d find it much easier to put images into writing.
W: That’s one of the reasons I’d talk to you. Since I know this is the time when you professors start planning what classes you want to teach next term, I wanted you to consider forming a class on nature writing. We could use the book you wrote as the class textbook.
M: I’m flattered that you think so. I suggested teaching a class on nature writing over two semesters ago, but the department head didn’t believe it would be popular with students.
W: Actually I know many students who want to sign up for it.
M: If you could get thirty students to send letters to the department head expressing support for a nature writing course, it might convince him to approve one.