Abstract
Gluon admixtures in neutral pseudoscalar mesons are considered to test the quark-line rule for the reactions pi p to eta Delta , eta n, pp to pi pi eta , etc. It is found that the experimental data on these reactions support the possibility of a small gluonium admixture in the eta and eta ' states. The results have also been used to predict some electromagnetic decay rates of the pseudoscalar glueball states l(1440) along with those of eta and eta '.