A sepal - petal, and a thorn

A sepal, petal, and a thorn,
Upon a common summer's morn—
A flask of Dew—A Bee or two—
A Breeze—a'caper in the trees—
And I'm a Rose! 
                                                        J19,  Fr 25 (1858)

Roses were the most prized flowers in Victorian gardens and literature. Dickinson prizes them as well and she uses them when she wants to express the utmost in beauty, completeness and vulnerability. Here she lists the elements that epitomize the Rose: sepal, petal, and thorn plus dew, bees, and breezes. 
     One of the key words is 'common': she is out on a walk, perhaps, on an ordinary day when she comes across this assemblage of ordinary elements and the whole comes alive into a glorious flower. Note that her list includes categories: the physical aspects of the flower, the time of year, the water, the pollinator, and the breeze that animates the whole. 
    The poem can also be read as transfiguration. She herself becomes the Rose. In her is the sepal protecting the precious flower within, in her the luscious petal of the flower itself —as well as the painful thorn that protects from depredations. Give her Dew, bees and a breeze ("dew-bee dew-bee dew...") and she is rose-like herself--and who wouldn't be?
     The poem is written in iambic tetrameter with a rhyme scheme of A A B (with internal rhyme) C C (with Rose a slant rhyme with trees). The final line, the punchline, is in dimeter, lending emphasis to the exclamatory word 'Rose!'