| Abstract: | Aphid stylet exudation during the period from dormancy to budbreak was studied in Tilia americana by means of detached branchesbrought from the woods into conditions of warmth and extendedphotoperiod. During physiological dormancy little exudationwas obtained. Thereafter until mid-March exudation was morevariable, but its onset accelerated progressively until mid-March,after which persistent exudation could be obtained from allbranches within 2 days. When the buds were removed from onebranch at this time, exudation persisted for only 5 days comparedwith 14 to 21 days for branches with buds. To account for theseresults it is suggested that a hormonal factor is produced bythe buds which results in sieve-tube activation, that the factoris virtually absent during physiological dormancy, and thereafterrequires a few weeks to become fully active. Determinations of sugar concentration, level of exudation, andbud dry weight indicated that exudation was most intense beforethe bud sinks were active and then rapidly falls off. It issuggested that the stylet acts as a sink competing with thenatural sinks for solutes from a limited region of the stem.Other interpretations are also considered. |
