CONIFEROUS ROOT EXUDATE

The literature on root ex?date is replete with studies of factors influencing the quantity and cycle of its production. For the most part, this work has been done utilizing herbaceous species or vines, but citations are also available on some of the broad-leaved trees. Root ex?date from conifers is rarely reported, but in the course of preparation of a thesis at the University of California it was convenient to test several young conifers for root ex?date production. Ex?date from decapitated conifers of several species, with sunflower's ex?date under comparable conditions for comparison, is given in the accompanying table. The table gives the species, the volume of root ex?date at each reading in cubic centimeters, and the time of each measurement. The data were collected as supplemental information to a series of transpiration studies and not as a designed experiment, which explains the different decapitating times for the various plants as indicated by 0.0 in table. The plants had been exposed to a series of humidities (90, 50, 70, 50, 30, 70, 90) at 75? F. for 22 days with 24 hours of light alternating with 24 hours of darkness. On October 4, the lights were turned off at 7: 30 a.m. and the 90% humidity maintained. The plants were then cut off as fast as leaf area measurements could be made, which resulted in a difference of two and one-half days between the decapitation of the first plant and the last.