http://en.wikipedia.org/wiki/Joseph_Gurney_Cannon#Speaker_of_the_House
Speaker of the House
Cannon wielded the office of Speaker with unprecedented power. At the time of Cannon's election the Speaker of the House concurrently held the chair of the Rules Committee, which determined under what rules and restrictions bills could be debated, amended, and voted on, and in some cases whether they would be allowed on the floor at all. As such, Cannon effectively controlled every aspect of the House's agenda: bills reached the floor of the house only if Cannon approved of them, and then in whatever form he determinedwith he himself deciding whether and to what extent the measures could be debated and amended.
Cannon also reserved to himself the right to appoint not only the chairs of the various House committees, but also all of the committees' members, and (despite the seniority system that had begun to develop) used that power to appoint his allies and proteges to leadership positions while punishing those who opposed his legislation. Crucially, Cannon exercised these powers to maintain discipline within the ranks of his own party: the Republicans were divided into the conservative "Old Guard," led by Cannon, and the progressives, led by President Theodore Roosevelt. His committee assignment privileges ensured that the party's Progressive element was essentially powerless in the House, and his control over the legislative process obstructed progressive legislation.