The powers of the two comitiæ as to the election of officers were differentiated. The comitia centuriata, at all stages in the history of the Roman republic, possessed the right of electing the highest officers of the republic--the consuls, prætors, and censors. The comitia tributa originally possessed the right of electing only the tribunes and the plebeian ædiles; at a later period they elected also the curule ædiles, the quæstors, the majority of the legionary tribunes, and all the inferior officers of state. The comitia tributa, in the later days of the republic, secured an indirect control over the election of the higher officers also, since the adoption of the legal principle that all Romans who sought the highest honors of the state must pass through a regular gradation of offices rendered it necessary for the comitia centuriata to choose as consuls and prætors men who had previously been chosen by the comitia tributa as quæstors and ædiles. It must be remembered, however, that the law relative to the order in which the various offices must be held was of a directory rather than a mandatory character; while in the main obeyed, it was, nevertheless, frequently violated. The various public offices here referred to will be discussed in the later chapters as each office first comes into existence in Roman history. It remains at this time to speak of the organization, powers, and authority of the Roman Senate, particularly as to its control over the work of the popular assemblies. The extent of the power of the Senate over legislation varied greatly in different periods of Roman history, and these differences were caused more by the existing political conditions, and by the relative strength of the aristocratic and popular parties in Rome, than by any express changes by legislation. At the very outset of Roman history we see the Senate existing as an aristocratic body, embodying in itself both the oligarchical principles upon which the Roman government was based, and also the patriarchal basis upon which the Roman family organization and later the organization of the Roman state itself had been built.