I do know the book I am seeking is not the Wonderful Flight to the Mushroom Planet, but it does have a similar premise. I read it in the 50’s. It is illustrated with black and white pencil illustrations. The basic story is some children build a wooden spaceship and in the process one of them finds a flexible silvery disc that is nailed to the nose of the wooden vessel. The children discover that it can actually fly and they also discover the alien the disk belongs to, it is his own ship.
During their adventures they go to a variety of planets, one with giant jelly plants and another with bubbles, one that traps the alien who has to be rescued by the children with the very same fingernails he was so critical of earlier.
I appreciate the help.
This sounds like ‘Rusty’s Space Ship’ by Evelyn Sibley Lampman (1957).
“As soon as Rusty and his sister build their wooden spaceship, a kid-sized lizard from outer space shows up looking for the metal saucer Rusty’s tacked onto the nose. The lizard lifts the whole thing by brain power, but he’s terribly absent-minded and can’t really remember where he’s going… so we get a tour of planets and moons of the solar system, filled with facts and fancy: on Mars one’s step is very light and springy, it is cold and dusty and windy, and — the canals are massive lines of ants going places!”
I think I remember reading this as a child. I think it involved someone names Mr. Basidium (or something like that related to mushroom etymology). I see Eleanor Cameron has written quite a few sequels to the original Mushroom Planet book. I don’t remember reading the one about Rusty’s Space Ship – though it does sound somewhat familiar.