A staple cartridge for use with a surgical stapler, said staple cartridge comprising: a cartridge body, comprising: a support portion comprising a deck, a proximal support end and a distal support end; a plurality of staple cavities defined within said support portion, wherein each said staple cavity comprises an opening in said support portion; and an implantable compressible portion positioned adjacent to said support portion, wherein said compressible portion comprises a distal compressible end; a retention member configured to releasably attach said distal compressible end to said distal support end, wherein a slot is defined between said retention member and said deck; and a plurality of staples, wherein at least a portion of each said staple is removably stored within a said staple cavity, wherein each said staple is movable between an unfired position and a fired position, wherein each said staple is deformable between an unfired configuration and a fired configuration when each said staple is moved between a said unfired position and a said fired position, and wherein said compressible portion is configured to be captured within said staples and may assume different compressed heights within different said staples when said staples are deformed between said unfired configuration and said fired configuration; characterized in that said retention member is movable relative to said compressible portion to removably capture said distal compressible end in said slot and between said retention member and said support portion. a cartridge body, comprising: a support portion comprising a deck, a proximal support end and a distal support end; a plurality of staple cavities defined within said support portion, wherein each said staple cavity comprises an opening in said support portion; and an implantable compressible portion positioned adjacent to said support portion, wherein said compressible portion comprises a distal compressible end; a support portion comprising a deck, a proximal support end and a distal support end; a plurality of staple cavities defined within said support portion, wherein each said staple cavity comprises an opening in said support portion; and an implantable compressible portion positioned adjacent to said support portion, wherein said compressible portion comprises a distal compressible end; a retention member configured to releasably attach said distal compressible end to said distal support end, wherein a slot is defined between said retention member and said deck; and a plurality of staples, wherein at least a portion of each said staple is removably stored within a said staple cavity, wherein each said staple is movable between an unfired position and a fired position, wherein each said staple is deformable between an unfired configuration and a fired configuration when each said staple is moved between a said unfired position and a said fired position, and wherein said compressible portion is configured to be captured within said staples and may assume different compressed heights within different said staples when said staples are deformed between said unfired configuration and said fired configuration; characterized in that said retention member is movable relative to said compressible portion to removably capture said distal compressible end in said slot and between said retention member and said support portion.