Midcap growth mutual funds’ 10-year performance trails slightly behind that of midcap core funds, which invest in both growth and value stocks, while midcap value’s has lagged well behind. A $10,000 investment made on June 30, 2005, in the average midcap growth fund would have grown to $23,995 by Sept. 9 this year, slightly behind the $24,415 that midcap core funds had the potential to generate, according to Morningstar Inc. data.