<P> Players are admitted to the junior tournaments upon the recommendations of their national tennis associations, on their International Tennis Federation world rankings and, in the case of the singles events, on the basis of a qualifying competition . The Committee of Management determines which players may enter the four invitational events . </P> <P> The Committee seeds the top players and pairs on the basis of their rankings, but it can change the seedings based on a player's previous grass court performance . Since 2002 a seeding committee has not been required for the Gentlemen's Singles following an agreement with the ATP . While the seeds are still the top 32 players according to rankings, the seeding order is determined using the formula: ATP Entry System Position points + 100% points earned for all grass court tournaments in the past 12 months + 75% points earned for the best grass court tournament in the 12 months before that . A majority of the entrants are unseeded . Only two unseeded players have won the Gentlemen's Singles: Boris Becker in 1985 and Goran Ivanišević in 2001 . In 1985 there were only 16 seeds and Becker was ranked 20th; Ivanišević was ranked 125th when he won as a Wild Card entrant, although he had previously been a finalist three times, and been ranked no . 2 in the world; his low ranking was due to having been hampered by a persistent shoulder injury for three years, which had only just cleared up . In 1996, the title was won by Richard Krajicek, who was originally unseeded (ranked 17th, and only 16 players were seeded) but was promoted to a seeded position (still with the number 17) when Thomas Muster withdrew before the tournament . No unseeded player has captured the Ladies' Singles title; the lowest seeded female champion was Venus Williams, who won in 2007 as the 23rd seed; Williams was returning from an injury that had prevented her playing in previous tournaments, giving her a lower ranking than she would normally have had . Unseeded pairs have won the doubles titles on numerous occasions; the 2005 Gentlemen's Doubles champions were not only unseeded, but also (for the first time ever) qualifiers . </P> <P> Since 2001, the courts used for Wimbledon have been sown with 100% perennial ryegrass . Prior to 2001 a combination of 70% ryegrass and 30% Creeping Red Fescue was used . The change was made to improve durability and strengthen the sward to better withstand the increasing wear of the modern game . </P> <P> The main show courts, Centre Court and No. 1 Court, are normally used for only two weeks a year, during the Championships, but play can extend into a third week in exceptional circumstances . The remaining 17 courts are regularly used for other events hosted by the Club . The show courts were in action for the second time in three months in 2012 as Wimbledon hosted the tennis events of the 2012 Olympic Games . One of the show courts is also used for home ties of the GB teams in the Davis Cup on occasions . </P>

What type of grass is wimbledon played on