I have read in several forums that cucumbers and cantaloupe do NOT...
I have read in several forums that cucumbers and cantaloupe do NOT cross-pollinate, nor is it possible, as they are separate species. Science may say no, but I promise you that I raised "cucaloupes"! They were very different when they started growing. I asked my husband several times what he planted in the space below the cucumbers, as it was supposed to be cantaloupe, but reminded me more of watermelon for its size and shape. He assured me it was cantaloupe, and showed me where he did, indeed, plant watermelon, and pumpkins. This "fruit" started out with white fuzz-like hair on it, over the green skin. Shortly, the fuzz disappeared and it began to grow long and oval, like a watermelon. It was dark green and never changed color. Finally, last Tuesday, my daughter and I decided to cut one of the odd fruits open. It was white on the outermost inside edge, then a coral color in the center, like cantaloupe, with coral colored seeds that looked like cucumber seeds. I wish I had taken a picture of it, but I didn't. I did not because my aunt told me cucumbers, planted near melon, will cross. I thought she was right and never considered she may be wrong. I don't think she was. It happened.
Thank you for your email to eXtension.
Based on everything I remember from the ancient history of my college horticulture and botany classes, as well as everything I've read ever since, there is no way that cucumbers can cross with melons or squash to form a "mutant" fruit. As you acknowledged, they are two completely different species, and short of using biotechnology (gene splicing) in a lab, there is no way they can affect each other.
This article from Iowa (somewhat dated) explains this better than I can: http://www.ipm.iastate.edu/ipm/hortnews/1996/8-23-1996/crosspol.html .
I do not doubt you saw something unusual in your garden. A more likely possibility is that what grew in that place was not something you purposely planted this year, but a "volunteer" plant from seed that were left in the garden from a rotted melon/squash/cucumber from last year.
All of the modern varieties of garden vegetables are hybrids. They are the results of crossing and recrossing different varieties, until breeders produce a plant that will give the characteristics they desire. However, if a seed from a hybrid melon or squash is saved and then replanted (either purposely or accidentally), then the plant that will grow will probably look nothing like its parent. It will produce something based on all of the genetic "mish-mash" that went into creating the hybrid in the first place.
When I was back in college in the late 70s, I worked with one of the world's leading experts on squash breeding. He brought me to a field, which had squash that ranged from baseball sized up to bucket-sized, and with every color and pattern you can imagine. No two plants produced anything even remotely alike. And that entire field was planted from the seeds of an acorn squash he'd harvested and saved the seeds from.
I've had cases like this in my local area, too. Some gardeners accidentally missed a rotting squash as they were cleaning the garden (or didn't clean up plant debris at all). One gardener I knew wound up with volunteer melons after a neighbor decided to have a seed-spitting contest over the fence. Other gardeners wind up with volunteer plants whose seeds had been dropped by birds, raccoons, and other animals.
All of these scenarios are much more likely than two different species suddenly being able to mingle their DNA together. And even if it was possible for these two species to cross, you wouldn't see the results of this until you saved the seeds from your normal looking melon/cuke this year and planted them next year. The edible fruit of a vine crop is part of the female flower from the plant you planted; only the seeds have any of the DNA from the male flower which gave off the pollen.
I hope this answers your question.