How do we say that cross polinated species show inbreeding depression and not self pollinating species?? Pls explain the lines marked.. what exactly is inbreeding depression??

How do we say that cross polinated species show inbreeding depression and not self pollinating species?? Pls explain the lines marked.. what exactly is inbreeding depression?? Inbreeding — When two individuals of a species, which have common ancestory are mated together. Most extreme form of inbreeding is self pollination. Inbreeding depression — Loss of vigour due to inbreeding. ross pollinated species shows inbreeding depression, but self pollinated species do not show inbr depression.