Final answer:
The question deals with the invalidation of power of attorney upon the principal's death, making any actions taken by the agent (in this case, signing a deed) legally ineffective posthumously.
Step-by-step explanation:
The subject of this question pertains to the validity of actions taken under a power of attorney after the death of the principal. When Smith, who had given Jones the power of attorney, died before Jones signed the deed, the power of attorney became invalid as it ceased to exist upon Smith's death. Without knowledge of the death, Jones signed the deed, but legally speaking, the deed would not be effective because the authority to sign on behalf of Smith was no longer valid after Smith's passing.
Estate law and the principles governing the execution of documents indicate that any such actions as the holder of power of attorney after the principal's death are of no legal effect. This is a fundamental concept in law where the death of an individual has various effects on legal rights and procedures such as the execution of a will, distribution of assets, and the performance under power of attorney.