Observations on Megasporogenesis and Megagametophyte Development in Paulownia sp and Sesamum indicum by Enzymatic Maceration Technique Embryo Sacs of Hevea brasiliensis and Carica papaya Isolated with Enzyme-Squash Technique Isolation and Identification of Viable Embryo Sacs in Several Angiosperm Species Isolation of Embryo Sac with the Enzyme-Squash Technique Isolation of Viable Embryo Sacs and Their Protoplasts of Nicotiana tabacum