26 USC 683 - Use of trust as an exchange fund

(a) General rule 
Except as provided in subsection (b), if property is transferred to a trust in exchange for an interest in other trust property and if the trust would be an investment company (within the meaning of section 351) if it were a corporation, then gain shall be recognized to the transferor.
(b) Exception for pooled income funds 
Subsection (a) shall not apply to any transfer to a pooled income fund (within the meaning of section 642 (c)(5)).