What form and structure did William Wordsworth use in his poem "Nutting"?

In William Wordsworth's poem, "The Nutting," the form and structure are not as obvious as in other poems.

Form present in poems deals with organizational aspects of the piece, concentrating on number of lines, meter for those lines, and rhyme (if any). Structure is defined as organization or design in a literary work, and may refer to divisions, such as acts, scenes, etc.

In form, "Nutting" is a poem written in blank verse: unrhymed iambic pentameter (ten syllables per line, with stress on every other syllable). It is a simple and unpretentious poem, something that may have been dismissed by some poets of Wordsworth's day. Similar to a pastoral poem, it concentrates on the wonders of nature as the young man travels through the woods to find hazelnuts. Poetry of the pastoral form (dealing with nature) is defined as:

...a poem that depicts rural life in a peaceful, idealized way for example of shepherds or country life.

Wordsworth created a new form of poetry with his writing of "Nutting." It was also "revolutionary" in that it was a "conscious challenge to classical norms of literature." Traditionalists may well have discounted the "intimacy" of Wordsworth's experience as too ordinary to have been taken seriously based on the poetic norms of the day. As one of the two first-generation Romantic poets (Coleridge being the second), Wordsworth would open the acceptable range of subject matter for poets, as well as using "a vernacular speaking voice." His words are presented much like common speech—which could not have been achieved with rhyme because the writing would have sounded too contrived. "Nutting" is delivered in an unpretentious manner, very different from the more sophisticated form consisting of obvious "literary" manipulations by the writer, typical of the more classical poets.

For structure, there are no obvious or specific breaks, however the action of the young boy in the poem (Wordsworth as a child) creates "natural" segments. Based on the poem's text, there appear to be three major parts to the young man's excursion into the forest.

We notice the first part when the lad sets out, dressed appropriately and equipped with the necessary tools, much like a young knight on a noble quest. As yet untried, the boy will do battle with nature to achieve the prize he searches for:

...of power to smile

At thorns, and brakes, and brambles, and, in truth,

More ragged than need was. Among the woods,

And o'er the pathless rocks, I forc'd my way...

At this point in the poem, the young man arrives at the place he has hoped to find, a "virgin scene" with clusters of hazelnuts, untouched. He does not disturb anything, but rests and relishes the magical moment.

A little while I stood,
Breathing with such suppression of the heart
As joy delights in; and with wise restraint
Voluptuous, fearless of a rival, eyed
The banquet, or beneath the trees I sate
Among the flowers, and with the flowers I play'd;

The magic cannot last; as with leaving childhood behind—like a rite of passage—the boy becomes a warrior and "attacks" that which had seemed so "worthy" only moments before.

Then up I rose,
And dragg'd to earth both branch and bough, with crash
And merciless ravage...
Of hazels...Even then, when, from the bower I turn'd away,
Exulting, rich beyond the wealth of kings
I felt a sense of pain...

These are the three segments: the journey, finding and worshipping the prize, and then, sadly, the harvest. This is the structure of "Nutting."

What is the theme of William Wordsworth's poem "Nutting"?

William Wordsworth's poem "Nutting" focuses on the various ways in which people (or even the same person at different times) relate to nature.

The speaker is reminiscing about his youth at the beginning of the poem. He remembers the day that, "in the eagerness of boyish hope," he set out on a nutting expedition. He was excited about the day, proud to be wearing shabby clothing on purpose so he didn't have to be careful of his apparel but rather could dig right into nature. He had no worries about bramble or thorns, "matted ferns" or "tangled thickets." He could plunge into them all and enjoy them to the utmost. Nature was his playground and his joy.

The speaker arrived at a pristine spot, a "dear nook / Unvisited" with no broken boughs or "withered leaves" and no devastation. The hazel trees stood tall and tempting, and flowers grew everywhere. The visiting boy experienced the blessing of a "sudden happiness beyond all hope." He lay on the ground, allowing all his senses to roam through the scene, seeing, hearing, touching, smelling, perhaps even tasting. This was a pure delight in the untouched natural world.

But then the boy remembered why he came to this perfect spot. He was going nutting. He forgot all about enjoying nature as nature itself and began to consider what nature could give to him. He crashed through the branches and boughs, shaking them and dragging them down to earth to grasp their hazelnuts. He destroyed the scene, mutilating the bower that just a few moments before he had delighted in. Only after the destruction was complete did he feel the pain of what he had done. Nature had become an object to be harvested, and he had harvested with glee, but the "dear nook" would never be the same again.

What aspects of Wordsworth's mind and poetic heart are illustrated in "Nutting"?

The most important thing to remember about Wordsworth is that he is a Romantic poet (not romantic like love, romantic as in the genre and time period).  Romantic artists (authors, painters, etc.) adhered to a certain set of beliefs.  Gone is the cold logic of the Age of Reason.  Romantics focus on emotional experiences.  They also focus on the individual. The Age of Reason was very much focused on the "good of the whole," while Romanticism puts the focus on a single person.

Another characteristic of Romantic art is the emphasis and focus on nature, or Nature.  For Romantic authors like Wordsworth, nature isn't only a thing; nature is more akin to an entity.  These authors believed that a person can have a deep, emotional relationship with nature, a sort of spiritual oneness in which knowledge, peace, guidance, etc. can all be attained through communing with nature.  A last main characteristic of Romantic literature is the theme of carpe diem.  The "seize the day" mentality is very important to this literary period.  Wordsworth and his writings exemplify this time period's characteristics so well that many textbooks will use Wordsworth to highlight literature/poetry that is typical of the genre.  

"Nutting" illustrates Wordworth's adherence to Romantic literature quite nicely.  For example: 

"When, in the eagerness of boyish hope,

I left our cottage-threshold, sallying forth

With a huge wallet o'er my shoulders slung,

A nutting-crook in hand; and turned my steps

Tow'rd some far-distant wood..."

"I came to one dear nook Unvisited, where not a broken bough Drooped with its withered leaves, ungracious sign Of devastation..."