Ok, (See the next paragraph to skip all this)  here is why we don’t recognize income on appreciated property, usually stock.  Rev. Rul 55-138 as modified by Rev Rul 68-69.  It was cited as an example in S. Rep. #91-552, at 80.  The issue was more important in those days because the max tax rate was 70%.  This seems to be the only support on point. Congress could have changed the law, but hasn’t.  So I go back to the theory that there has not been an event for recognition/realization which is usually required in other tax transactions.  Rev Rul 55-138 doesn’t seem to be on point though, Revenue Ruling 55-138, C.B. 1955-1, 223, holds in part that the fair market value of property that is contributed to a charitable organization will be the replacement cost to the donor in his most favorable market.   Rev Rul 68-69 established another rule than replacement cost to value the donation and doesn’t seem to be on point either. 

Still 55-138 was cited in some cases where it was questioned if a donation of agricultural products triggered income.  At first, the rule was cited as: I.T. 3910, supra , holds (1) that the fair market value of agricultural products contributed by a farmer or other producer to an organization described in section 23(o) or section 23(q) of the Internal Revenue Code of 1939 is includible in the gross income of the donor.  Then the ruling cited a bunch of cases contrary to that proposition, and it held than that “In the light of the above cases it follows that no income is realized by a farmer or other producer by reason of his contribution of farm or other products to an organization described in section 23(o) or section (q) of the Internal Revenue Code of 1939.

So that is about as close as I can come to a citation.

BNA portfolio 521-3rd A-113 (2008) and Parker tax pro library.