The above-ground portions of 2-yr.-old exptl. seedlings of Pinus coulteri growing in containers filled with soil to which no water had been added for over 10 mos. and with the soil surface sealed with grafting wax were sealed in a plexiglass chamber fitted with an Aminco-Dunmore temp., and humidity-sensing unit attached to a micro-ammeter. With the exptl. plants sealed in the chamber, the relative humidity was raised to the desired value (usually about 98%) and readings of the r. h. in the chamber made at intervals for a period of 96 hrs. The aerial portions of test plants were able to remove moisture from the atmosphere, as evidenced by a drop in the r. h. to as low as 84%. This period of "negative transpiration" which lasts about 24 hrs. was followed by a period of positive transpiration during which the r. h. again rose. Two types of controls are run, the 1st using an empty chamber, the 2d using pine seedlings which had been well-watered throughout their life. Both control and exptl. plants were exposed to a current of air from an electric fan for 48 hrs. before testing to insure a water deficit in the aerial parts of the plants. In neither of the types of controls was there any decrease in humidity in the chamber. The ability of these plants grown on arid soil to remove moisture from a humid atmosphere may account for the fact that pine and certain brush spp. can survive long periods of drought on shallow soils which are often at the wilting point for several mos. during late summer. These conditions may be observed on the lower mountain slopes in Southern California. Five-year humidity studies show that during the period from July to Oct. the r. h. at an altitude of 1500 ft. in the San Gabriel Mts. reached a value of over 90% on an avg. of 18 days/mo. with an avg. duration of 8 hrs. of high humidity/day.