When a general power is defectively executed, equity will not aid the appointee, unless a valuable consideration has been paid,227 but, where there are defects in the execution of a special power, the aid of a court of equity will be given,228 if there has been a substantial compliance, and such defects as the omission of the requisite number of witnesses will be supplied;229 and so, where the execution has been by will instead of by deed, it will be held good.230