Gourds have always been important in human culture. In the late Middle Ages, schoolteachers would cut Latin words onto the surface of squashes and gourds as an aide-memoire for young children. This is, in fact, where we get the very word 'word', via the earlier Anglo-French guord (cf. Guillaume > William, guard > ward), which in turn is simply a variant of gourde or coorde (Latin cucurbita), and from which we have gourd and courgette.
Boccaccio was well aware of the symbolic significance of gourds, as we discover in Decameron 8.9, one of the work's pithiest novelle. In this story, two painters named Bruno and Buffalmalco—a recurrent duo—play a trick on Simone, a greedy and foolish physician from out of town. They convince him that they are secretly wealthy, thanks to the machinations of a cabal of necromancers; they encourage him to come along to a meeting, then push him in a ditch at night. So far, so mediaeval. But it is the imagery that here interests us.
Maestro Simone arrives back in Florence from Bologna (the university for law and medicine par excellence), where he settles in a street named Via del Cocomero—'Watermelon Road'. When Bruno addresses him early on, he calls him zucca mia da sale, 'my salt squash', and praises vostra qualitativa mellonaggine da Legnaia. Legnaia is a region of Florence then noted for its large pumpkins, and 'mellonaggine', which connotes stupidity, comes from the mellone or melon. Later on, Buffalmalco addresses Simone as Pinca mia da seme. Pinca, the etymological dictionary of Pianigiani (online here) tells us, is an archaic word for a species of cetriuolo or cucumber, and da seme means 'full of seed'. Finally, Buffalmalco mocks Simone: it is evident that the physician 'non apparaste miga l'abicí in su la mela, come molti sciocconi voglion fare, anzi l'apparaste bene in sul mellone, ch'è cosí lungo'—'did not learn the ABC on an apple, as so many idiots do, but instead learned it well on a melon, which is rather longer'. (J. M. Rigg's 1903 translation perhaps renders the pun best: 'twas on no pippin, as many a dolt does, but on the good long pumpkin that you learned your A B C'.)
So, what's with all the squashes? Wikitalia's article on the melon claims that it was originally considered a symbol of fecundity because of its large quantities of seed, later coming to symbolize a wild, generative capacity, opposed to intelligent reason—a fool. 'Uno stolto veniva chiamato mellone e una scemenza, mellonaggine'. But it is not just the melon—the entire family of Cucurbitaceae recurs through the novella as an unstated leitmotive, tying Simone's foolishness to his environs (cocomero), his education (mellone), and his interpersonal relations (zucca and pinca). He cannot escape it.