Transpirational Surges in Tamarix and Eucalyptus as Measured with an Infrared Gas Analyzer

In many transpiration studies a method has been used in which a leaf or twig is severed from a plant and transferred quickly to a balance where subsequent weight losses are followed. Use of this method has been reviewed recently (1, 5). One objection to the method is that no information is obtained as to behavior of the leaf immediately before and after excision. Thus estimation of the quantity of most interest, transpiration rate of the intact leaf before excision, is difficult. Andersson, Hertz, and Rufelt (1) developed an apparatus in whiclh a corona-discharge hygrometer recorded the absolute humidity of air streaming over a single leaf. Thus they were able to obtain continuous records of transpiration before, during, and following excision of a leaf. With the species tested (Solanuni lvcopersicumi., Thunbergia alata, Citrus sp.) transpiration increased rapidly immediately after excision and then declined. Their observations raise serious doubts about the usefulness of the cut-andweigh method for estimating transpiration rates of intact leaves. In the present study, their tests were repeated with slightly different apparatus and two different species and with essentially similar results.