What is the significance of allies baseball mitt to the extent that Holden decide to write about it for Stradlater´s papers?

Allie's left-handed baseball represents Holden's love for his deceased brother as well as Allie's authentic nature. Allie had covered the glove with poems written in green ink, a testament to Holden's intelligence and perhaps lack of athleticism.Holden only shares it with one of the only people he believes is authentic, Jane Gallagher. In many ways Holden idolizes the people that he has lost. They become "real" manifestations of what other people are not. Holden uses Allie as a comfort and an example of what he seeks but cannot find in others or himself. The glove is a personification of this.