The definitive statement on Amendments in the Senate:
The Amendment Process
Once a bill or resolution is before the Senate, it is subject to the amendatory process, both by the committee reporting it and by individual Senators offering amendments from the floor. A committee amendment reported as a total substitute (striking all after the enacting clause and inserting new language for the entire bill) for the pending measure is always voted on last, inasmuch as once a total substitute is agreed to, further amendments are precluded. With this exception, however, committee amendments take priority and are considered in order as they appear in the printed copy of the measure before the Senate. The only amendments from the floor in order during the consideration of these committee amendments are amendments to the committee amendments or sometimes to the part of the bill the committee amendments would affect.
Once the committee amendments have been disposed of, however, any Senator may propose amendments to any part of the bill not already amended, and while an amendment is pending, an amendment to the amendment is in order. By precedent, an amendment to an amendment to an amendment, being an amendment in the third degree, is not in order. However, the first amendment in the nature of a substitute for a bill, whether reported by a committee or offered by an individual Senator, is considered an original question and is amendable in two more degrees.
There are certain special procedures in the Senate which limit the amendatory process. For example, during the consideration of general appropriation bills, amendments are subject to the strictures of Rule XVI under which it is not in order to offer non-germane amendments or amendments proposing new or general legislation or increasing the amount of an appropriation if that increase has not been previously authorized or estimated for in the President's budget. Likewise, when operating under a general unanimous consent agreement in the usual form on a bill or resolution, amendments must be germane. Germaneness of amendments is also required once the Senate has invoked cloture; in addition, any amendments considered under cloture must have been submitted in writing before the Senate's vote on cloture.
http://www.senate.gov/legislative/common/briefing/Enactment_law.htmNo what, pray tell, could be clearer than that? (Yes, I am kidding. Yes that reads like someone cuts the words out of the newspaper, threw them in the air and then picked them up and wrote them down as they appeared. Still, I sort of understand this. Pray for me.)
That second paragraph is a masterwork. One rarely finds something that unreadable just put out there as a definition. Wow!