How does Ruku change throughout the novel?

In classic literary fashion, the changes that Rukmani (Ruku) go through throughout the novel are presented in broad sweeping images in the first few chapters, foreshadowing what will come. Ruku begins narrating the story as an old woman with a son who is not her own and eyes that are growing too dim to see the world clearly, although this dimness does not apply to her life-visions that appear before her with such vividness that she reaches out to touch them as though they were present with her and tangible.

Ruku goes through many changes throughout the story, which begins in her girlhood when she has the trusting confidence of a well loved young girl (under twelve years of age) and which ends in her agedness when she has the worldly wisdom of an old woman who has managed to remain without bitterness and who, living seemingly countless times in the face of hopelessness, pursued an object to give her reason to reclaim hope. 

Work without hope draws nectar in a sieve,
And hope without an object cannot live. (Coleridge, "Work without Hope")

As a momentary aside, Coleridge's couplet, borrowed from his 1825 sonnet "Work without Hope" and used by Markandaya as the story's epigraph, is representative of Ruku's life experience and explanatory of her motivation for claiming Puli as her own, and it can be paraphrased (restated in prose language) like this: He has work but has no hope, so his reward is the minuscule bit of nectar trapped in a sieve, for hope without work (an object) cannot live. Another way to paraphrase this difficult couplet is this: Work is hope; without hope, work is lost sweetness. Hope is purpose; without purpose, hope cannot live. Understanding this couplet correctly leads to understanding Ruku and her story correctly (misinterpret this couplet and you will misinterpret Ruku).

To return to Ruku, in a subtly incorporated flashback we are shown that as a young girl, Ruku loved, believed in and respected her father and mother, even though as the fourth daughter, she might have an inadequate dowry at her marriage. When she was then married without any dowry at age twelve to a tenant farmer and taken to live at a great distance from them in a mud hut built with his own hands, she fully understood that her father, even though he was headman of their village, had lost his wealth and its equal weight in power to the "Collector" who now governed the village and now held the power and wealth.

At her marriage, Ruku changes from a happy, well-beloved girl to a young bride ill equipped for her new life without servants and plenty and who was filled with fear at the stark barrenness and poverty of her new surroundings, even though Nathan, her new husband, was filled with hope and joy because of the ample harvest that filled one room of their mud hut. As time passes and she learns the depth and tenderness of her husband's caring heart and loving, patient ways, Ruku changes again. This time she discovers the joy of a newfound womanly love toward her husband, toward her work (especially tending her garden, which grows with the same strength she herself grows with) and toward the new life stirring within her:

"You are not a child any more," [Nathan] said at last. "You have grown fast since the day we were married...." While the sun shines on you and the fields are green ... and you have ... a sweet stirring in your body, what more can a woman ask for? My heart sang and my feet were light....

Another change overtakes Ruku when their firstborn is a girl instead of the hoped for boy who would work side by side with his father and complete his work, work begun in Nathan's youth and continued in his son's youth. Her sorrow and shame over this cultural failure was deepened as for seven years she and Nathan produced no further heir. Her encounter with Dr. Kennington, the "foreigner" to whom Ruku went in secret for she "had not wished [her] husband to know that [she] was putting [herself] in the hands of a foreigner," provided her with help that ushered in the birth of not one son but many, giving Nathan the object of his hope in an ample, virile family.

The later changes in Ruku came as a result of the departure of children, family tragedy and "all the clamor which invaded [their] lives later." As work lost hope because their land was lost and as hope lost purpose as the object of hope was withdrawn, Ruku--always faithful to her early way of seeing and doing things she had never seen or done before as after Nathan praised her for her first beautifully grown pumpkin--exerted her resolve and found in Puli, the unwanted leper, her work, her object and her hope reclaimed.

The last of the changes that occur throughout the novel in Ruku as she continues on to the end of her life--warm with visions of past goodness and love from those surrounding her--is that she rejects all bitterness bred of despair and sorrow and embraces the object of love and hope as she works to keep her promise to Puli while holding to her memories of good and love.

[N]ot all the clamor which invaded our lives later could subdue the memory or still the longing for it. Rather, [the later clamor] has strengthened [the memory] ....