In Paul Zindel's The Effects of Gamma Rays on Man-in-the-Moon Marigolds, the character of Ruth is the most affected by the toxic influence of her mentally unstable mother, Beatrice Hunsdorfer.
Evidence from her sullen and deeply-troubled nature can be found in three facts: first, in her nightmares, second, in her seizures, and then in her mood-swings.
In Act I it is exposed that Ruth has suffered a traumatic event involving Mr. Mayo, a former paying tenant. Apparently Ruth found the man either dead or in a near-dead state, which caused her to go into a seizure. This causes her to have recurrent nightmares about that event.
Ruth: He's after me...It was the dream, with Mr. Mayo again...They say I came out of my room...and I started down the stairs, step by step...and I heard the choking and banging on the bed and...[ENDS]
Her nightmares are equal to her seizures, which are apparently controlled by Beatrice's summoning of Ruth to "not let herself go". Yet, there is a lot more: Ruth's obvious state of mind leads her to shift back and forth in her moods. At the beginning of the play she humiliates Tillie by telling her mother how everybody laughed at Tillie's wardrobe while she was cranking up the model of an atom at a school assembly. She even supports those who give her sister grief, such as Chris Burns,
Chris Burns says to me- "She looks like the one that went to the looney doctors." I could have kissed him there and then.
Yet, when Tillie is publicly announced as a nominee for the Science fair, Ruth had nothing but praises for Tillie, stating over and over how proud she was of "her sister".
Ruth also seems to be quite loose. Her mother's own words about Ruth say as much when she suggests that Ruth must be at the school yard "running around in her brassiere".
Aside from other flaws, a salient one in Ruth is her tendency to tell lies and exaggerate things. She exaggerates about everything, from Janice Vickery's cat project, to the way in which people supposedly speak behind her mother's back. In Ruth's own seemingly-proud words about her "history"
..it says that I exaggerate and tell stories, and that I am afraid of death and have nightmares...and all that stuff.
Yet, after doing a close reading of Ruth's character, it is safe to conclude that all of her talk is precisely that: just talk. She just needs to act tough in front of her mother because, after all, Beatrice seems to be the family's biggest bully. Although Ruth tries to pair up with her mom, she falls flat in the end: Beatrice is the most dangerous character of them all.
The most noteworthy trait that both makes and breaks Ruth is what seems to be her defense mechanism: the seizures that overpower and weaken her. It is after Ruth finds out that her mother has killed her pet, where Ruth's defenses seem to shut down to the point of finishing her. It is almost as if Beatrice had thrown a thunderbolt at Ruth with her anger and caged-up frustration, and that this thunderbolt is meant to directly attack Ruth. After all, killing the rabbit is Beatrice's most vindictive and evil manifestation. This is why the last seizure that Ruth has in the play is also the most dramatic:
Ruth's eyes roll in her head..and the trembling of her body becomes pronounced throbbing. She drops the rabbit with the towel covering it.
Therefore, Ruth is a direct victim of her mother, and her victimization is evident in her actions, thoughts, and in her defense mechanisms.