Uktzin 2:7

The green leaves of vegetables combine but the white don’t. Rabbi Elazar bar Tzadok says that the white leaves of cabbage do combine because they’re edible. The same is true for those of lettuce since they protect the edible part.

Uktzin 2:8

Regarding onion leaves and onion shoots, if there’s sap in them, they must be measured “as is”; if there’s empty space in them, they are squeezed tightly. Spongy bread is measured “as is”; if there’s empty space in it, it’s squeezed tightly. The flesh of a calf that has swollen and the flesh of an old animal that shrank are measured “as is.”