In a medium bowl, mix flours, wheat germ, sugar, salt and soda. Stir in water and butter until smooth dough forms. Divide in half; cover; let stand 10 minutes. Place half the dough on a lightly oiled 17 x 14 inch baking sheet; roll out to a 16 1/2 inch x 13 1/2 inch rectangle. Prick all over with a fork, cut in 1 1/2 inch squares, brush with water and sprinkle with additional salt (opt.). Bake at 400 degrees for 8 minutes until crisp but not overbrowned. Remove to racks to cool. Repeat with second half.