This section is from the book "Real Estate Principles And Practices", by Philip A. Benson, Nelson L. North. Also available from Amazon: Real Estate Principles and Practices.
All improvements become the property of the landlord when made. It is proper in some cases to provide that some or all improvements may be removed at or prior to the expiration of the lease. Fixtures and machinery installed by the tenant are usually considered personal property and are removable when the tenant removes. The lease usually provides that no alterations to the building shall be made without the consent of the landlord.