I doubt this becomes a 'hybrid', merely a grafted pair. I'm sure in this case it is mostly for aesthetic reasons. Perhaps Jamshed will correct me if I am wrong.

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This plants is Gymnocalycium Mihanovichii
The Typical species was discovered near Bahaia near Brazil
Plants has color isGrayish-green or reddish but there is also a red or yellow form known as rubrum, which is frequently seen grafted onto Hyloceres The plant is exposed to Gamma rays, which remove what chlorophyll it normally possesses; it then grows at is expense of the stock gradually losing its bright color. It is impossible to get the stem or any basal shoot to take root.
Jamshed

Very interesting album!! I had no Idea this is how it was done.. I have one just like it.. I did not know it was grafted.. I thought it grew like that lol!!

And this really grows into a hybrid cactus variety??? Or is this for another reason?? This was a very interesting album. I'd like to know more.