Apples -or not?
Magritte‘s work frequently displays a collection of ordinary objects in an unusual context, giving new meanings to familiar things. The use of objects as other than what they seem is typified in his painting, The Treachery of Images (La trahison des images), which shows a pipe that looks as though it is a model for a tobacco store advertisement. Magritte painted below the pipe “Ceci n’est pas une pipe” (“This is not a pipe”), which seems a contradiction, but is actually true: the painting is not a pipe, it is an image of a pipe. It does not “satisfy emotionally”—when Magritte once was asked about this image, he replied that of course it was not a pipe, just try to fill it with tobacco.
Magritte used the same approach in a painting of an apple: he painted the fruit and then used an internal caption or framing device to deny that the item was an apple. In these “Ceci n’est pas” works, Magritte points out that no matter how naturalistically we depict an object, we never do catch the item itself. (Wikipedia)
The shown letter is showing the Magritte´s apples with a annotations how to configurate them. When I read the website http://www.mattesonart.com/1961-1967-later-years.aspx
I recognized the painting which belongs to this letter