Most People Think That Deciduous Treesshed Their Leaves In Order to Avoid a Winter, or a Tropical Dry Season. and Sothey Do. But This Is Not the Only Reason. They Also Shed Their Leaves Toachieve a Break In Their Parasitism, and to Resuscitate Their Biochemicallocks. This Additional Function of Leaf-Shedding Explains Several Conundrumsthat Baffled Botanists For Years. For Example, It Explains Why a Temporaryresistance Should Evolve In a Tree That Lives For Centuries. It Also Explainswhy a Tree Such As Rubber (Heveabrasiliensis) Should Be Deciduous, and Have Vertical Resistance to Adisease Called Leaf Blight (Microcyclusulei), Even Though It Occurs Wild In the Amazon Valley, Which Iscontinuously Warm and Wet. and It Explains Why the Members of the Mendelianschool Could Not Find any Single-Gene Resistances In Various Important Cropsderived from Wild Plants That Have Continuous Epidemics, Such As Sugarcane,Citrus, and Olives.