Pig. 152. Diagram showing a method of double crossing maize to secure maximum yield from »^i\ 

 plot and general crop. Four different inbred strains (shown in the top row) are cros.s«'d in pairs, pro- 

 ducing the two vigorous but unrelated Fi hybrids shown in the middle rt)w. By rros.sinK Ihcso with 

 each other, an entire crop of Fi seed of high productiveness is secured. (After East and Jones.) 



