Various treatments were given to 8-month-old bristle-cone pine seedlings; and it was found that supplementing the winter day length with a 250-watt heat lamp in order to give a total of 16 hours of illumination proved most effective. The lamp was placed about three feet above the seedlings, and the temperature in the growth chamber was kept at about 70'F. Those which received a short (circa 21 days) drought stress period in August of the third growing season showed up having one more growth ring than the control seedlings, that is four growth rings instead of three. Also seedlings which received a two week drought stress period in August of the fourth growing season showed a similar extra growth ring. The bearing of this on the estimates of the age of the bristle-cone pine forest is discussed. Under the San Francisco type of both spring and fall rainfall with a relatively dry perod in the summer the young forests on the White Mountains would have grown an extra ring per year quite often. Accordingly it is believed that the presumed 7100 year age postulated for these trees by Ferguson would be reduced to about 5600 years, on the assumption that extra rings would be formed by stress during about 50% of the years between the end of the Flood and about 1200 A.D.