Does anyone know about lemon trees, My seedling isdoing strange things?

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I planted a few lemon seeds and one of them took Its about 2 years old and has started putting out branches. Norman. right? But it seems to be perspiring a lot of sap. the bottom of all the leaves are sticky and theentire leaf of the bottom ones are also, from the sticky liquid dropping onto them. Is this normal, or is my little plant sick?