By October 11, 1912, the train carrying Abdu'l-Baha had made its way to California. In Califormia, Abdu'l-Baha most certainly saw a large number of fruit trees. Sometimes, Abdu'l-Baha would use the image of a fruit tree when stating a spiritual concept.
Here is a statement that Abdu'l-Baha made while he was in the United States:
What are the fruits of the human world?
They are the spiritual attributes which appear in man.If man is bereft of those attributes, he is like a fruitless tree.
One whose aspiration is lofty and who has developed self-reliance
will not be content with a mere animal existence.
He will seek the divine Kingdom;
he will long to be in heaven
although he still walks the earth in his material body,
and though his outer visage be physical,
his face of inner reflection will become spiritual and heavenly.
Until this station is attained by man,
his life will be utterly devoid of real outcomes.
The span of his existence
will pass away in eating, drinking and sleeping,without eternal fruits, heavenly traces or illumination
-- without spiritual potency, everlasting life
or the lofty attainments intended for him
during his pilgrimage through the human world.
~ Abdu'l-Baha, The Promulgation of Universal Peace, p. 336