Matthew 13:38

And the field is the world; and the good seed, these are the sons of the kingdom; and the tares are the sons of the evil one.

The fact that the tares did not appear until fruit was "brought forth" (Matthew 13:26) shows that they were indistinguishable from the wheat until that time, a fact strongly indicating that they were "in the church," else they could not have been confused with the wheat. The "tares" were actually "darnel" (English Revised Version (1885), margin), a type of bastard wheat bearing a close resemblance to the noble grain and impossible to detect until harvest. It is this proximity of the tares and wheat and the lack of identification separating them that forces one to look "in the church" for the area under consideration.