Scallion seeds are also known as green onion seeds, salad onion seeds, and spring onion seeds. They are botanically similar to regular onions, but do not for the swollen bulb like Spanish onions. Scallions are cold hardy and can be grown all winter beneath a cloche cover or even on a bright windowsill. Onions in all forms (as well as leeks, chives, and garlic) derive their pungent aroma from complex sulfur compounds, which are present from the seedling stage onwards. When onions are cut, their cells are broken and they release enzymes which then break down sulfoxides within the onion tissue. This results in the release of sulfenic acids. A second enzyme within the onion rapidly converts the sulfenic acids to a volatile substance known as lachrymatory factor gas. When this stuff hits your eyes, it stings, and your eyes immediately begin to tear up in an attempt to rinse themselves clean. The effect can be reduced or prevented by slicing onions under running water, or simply using a fan in the kitchen to disperse the gas.