The 21-year-old Marson led all Phillies Minor Leaguers with a .394 average in 26 games last month. Among his 37 hits were eight doubles and two homers. He scored 20 runs and drove in 37. At the end of May, he was leading the Eastern League with a .356 average and a .500 on-base percentage.
Marson hit in 24 of 26 games last month and had nine multi-hit games. He also set a personal high with six RBIs against Akron on May 18. He batted .412 over his last 10 games in May.
Through Monday, Marson is hitting .354. He has walked 34 times and struck out 33 times.
The right-handed hitter was a fourth-round selection by the Phillies in 2004 out of Coronado (Ariz.) High School.
"Lou's as mature a hitter for his age as I've seen," said Reading manager P.J. Forbes. "He doesn't give away at-bats, doesn't give in. His progress is outstanding, considering this is his first year above A ball.
"He's been a big RBI man for us, too, hitting in the four-hole. Behind the plate, he handles the staff well, and we continue to work with him on calling a game. He has the potential to be a very special big league player."
Walls, 24, did not allow a run in 11 appearances in May. He was 1-0 and recorded an organization-high seven saves. In 15 1/3 innings, he allowed six hits and five walks. He struck out 19 while holding opposing batters to a .122 average.
Of the Threshers' 14 wins last month, Walls saved seven and won one.
For the season, he is 1-0 with a 0.88 ERA and nine saves. Opponents are hitting .152 in 30 2/3 innings, and he hasn't allowed a run in 16 of his 19 appearances. The last run he allowed was on April 28, against Tampa.
The right-hander was selected in the 10th round in 2006 out of North Carolina State University. He did not pitch at all last year because of surgery on his right shoulder.
"He's a fastball [92 to 94 mph] and cutter [89 to 91 mph] guy," said Steve Schrenk, Walls' pitching coach. "The cutter is his out pitch. Throws strikes. He's very aggressive and has been our guy at the back end of the 'pen. Extremely consistent. He's come back from shoulder surgery and has turned into a big prospect."
Larry Shenk is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.