150 PLANTS AND MAN 
Zea (Maize). The value of these to the human race is 
incalculable, and some of them have been in cultiva- 
Fic. 25..-WILD CABBAGE (BRASSICA OLERACEA). 4. 
tion for at least five thousand years. In some of them, 
indeed, the native form is now unknown, the improved 
