beam biology botany cell cross-section culm haulm lime tree linden magnification microscope plant stalk tree abstract Capsella Capsella bursa-pasto embryo enlargment family Brassicaceae magification micro mustard seed Shepherd's-purse anatomy cells female follicle Graaf health human oocyte ovarian science bean Bell Bean Broad Bean Faba Bean Fava Bean Field Bean food Tic Bean Vicia faba