* Company adding 36 new greenhouses * Will add space to house approx 2,000 workers April 23 (Reuters) - Flush with cash, global seed developer Monsanto Co. said Tuesday that it will spend $400 million to expand a research center focused on development of new genetically altered crops. Monsanto said it will add 36 new greenhouses, additional offices and laboratory space as well as additional plant growth chambers to an existing 1.5 million-square-foot site in Chesterfield, Missouri, to facilitate development of its seed and genetic trait product development. The greenhouses and plant growth chambers can be programmed to represent any climate around the world. Earlier this month, Monsanto said it expects to sell a record amount of corn this year, and said that it had $1.6 billion in free cash flow, with full-year free cash flow seen at $1.8 billion to $2 billion. The Creve Coeur, Mo.-based company plans to begin work this summer and expects to add 675 jobs related to the expansion over the next three years, officials said. Monsanto currently has approximately 1,000 employees at its Chesterfield site, and will be able to house 2,000 technology employees when the expansion is completed. The company already has 250 laboratories, 122 plant growth chambers and two acres of greenhouses at the location.