As mentioned above, the Legislature convenes in regular session for only 140 days (counting Saturdays and Sundays) every two years. The session begins in January of odd numbered years - after the November elections two months earlier. The legislature convenes on the second Tuesday in January and adjourns in late May or early June.
All legislation that has not been approved by both houses by the last day of the session is dead. At the end of the regular session there is always a crush of legislation that is passed in a flurry of activity. This can lead to the passage of bills that have not been thoroughly reviewed by both of the full chambers, leaving open the possibility of slipping in provisions (sometimes unrelated, or non-germane) that favor special interests.
After the regular session the governor can call as many special legislative sessions as he or she may wish. The governor sets the agenda for these sessions, which usually focus on extremely important state business. The threat of calling a special session gives the governor power to get the legislature to deal with pressing issues, and provides a useful tool for governors - though one that is not without risks.
Each two year period for which a single cohort of representatives and senators are elected has been identified by a unique number dating back to the beginning of statehood. For instance, the legislature that convened in 2009 was the 81st Legislature, followed by the 82nd legislature in 2011.
The 140 day session is an extremely short period of time to conduct the state's business, especially considering the large size and considerable diversity of both the population and the economy of Texas. The short session is in part a reflection of the Reconstruction era during which the current Texas Constitution was written. After the excesses (real and perceived) in the use of governmental authority by the Radical Republican administration of Governor E.J. Davis, a convention was called that rewrote the constitution along very restrictive lines. The short legislative session - along with the limited powers given the Governor - exemplifies the attempt of the Constitution's authors to restrict the ability of the government to govern too much.
2 Texas State Historical Association, The Handbook of Texas Online, link:http://www.tsha.utexas.edu/handbook