Can I access Google Now from any app I am in on my iphone 6 , and if so, how?

[iMore Question]

For example, if I am in my app for my Evernote, and I say Ok Google, nothing happens.

It only works if I am in the Google app.

 

[Just_Me_D]

I doubt it, but I can't say because I do not use Google Now. Having said that, why would Apple allow Google to replace Siri, it's own flagship assistant?