In this poem "Lycidas'" by John Milton. I need to analyze quote,show the key image, symbol and theme.the Quote is "Fame is no plant that grows on...

This is an excellent question, focusing in real detail on
the actual phrasing of the poem.

1. A key image in
   this line involves the reference to a “plant.” The plant image is appropriate to the
   poem in several ways. The poem opens with plant imagery, and the entire poem is set in a
   rural landscape full of plants and imagery of growth. Various other plants, especially
   flowers, are mentioned in the poem.  Since plants are associated with life, and since
   this is a poem that meditates on the sudden loss of life, the plant imagery is highly
   appropriate.


2. The plant, as a symbol of life, is
   appropriate to Milton’s concern with achieving a kind of life, and a kind of fame, that
   will not die. Plants usually die off once a year, but Milton is seeking a kind of legacy
   that will not fade and will not die.  Such a legacy can only be achieved (he later
   suggests) with the help of God and through commitment to God. Plants periodically die,
   but the kind of life and legacy Milton seeks is
   eternal.


3. The plant imagery is appropriate to the poem’s
   larger themes, one of which involves trying to make sense of death.  Just as plants seem
   to die but later revive, so the speaker of this poem manages to convince himself by the
   end of the work that his friend Lycidas is not truly dead but has “mounted high” (172),
   into heaven with God. Just as plants are reborn, so Lycidas has also been revived and
   resurrected.