iambic pentameter
This line is in iambic pentameter because it has ten syllables that alternate unstressed then stressed.
 u    /    u     /     u     /     u   /   u    /
To | swell | the | gourd,| and | plump | the | ha | zel | shells
 1   2    3    4     5     6    7   8   9   10
When trying to identify meter and rhythm, start with two syllable words-this will help identify where some stresses sit in the line.