The Gemora says that one is Chayov for moving something from the ground from which it gains nourishment although it was not attached. From this, the Sforno (Parshas B'shalach 16, 27) concludes that the collection of the 'Mon' on Shabbos would involve a definite Chilul Shabbos. My question is: Where do we find the 'Mon' gaining any nourishment from the ground?
The Gemara (at the beginning of 108a) says that even though something does not actually gain nourishment from the ground on which it rests (such as the fungus that grows on the handle of a pitcher), since that is its normal way of growth, one will be Chayav for detaching it from there. The same applies to the Man; its normal way is to collect on the ground and thus that is considered its normal place of growth, and taking it from there constitutes the Melachah of Tolesh.