gems don't get found

Hy!

I have the following problem;

In config/environment.rb i have config.gem 'wysihat-engine' (or anny
other gem)

When i "rake gems:install"
(in /home/user/rails_apps/res-test)
gem install wysihat-engine
Successfully installed wysihat-engine-0.1.13
1 gem installed
Installing ri documentation for wysihat-engine-0.1.13...
Installing RDoc documentation for wysihat-engine-0.1.13...

But app won't start;