The expression, ‘leprous hide’, refers to the bark of the tree which looks like the skin of a leprosy patient. It is brown, dry and rough.
Leaves grow from its ‘leprous hide
The poet here personifies the tree by describing its bark as ‘leprous’. He uses a medical term to personify the tree.
The expression is ironical. Leprosy usually eats away the body and hampers normal growth. But here, leprous hide is a source of growth. It bears the leaves that produce food. It is not a symbol (image) of decay, but of growing life. This kind of image certainly makes the poem a modern one.