Henry Ernest Dudeney/Modern Puzzles/149 - A Tree-Planting Puzzle

by : $149$

 * A Tree-Planting Puzzle
 * How do you plant $13$ trees so as to form $9$ straight rows of $4$ trees each?


 * Here is an arrangement that gets you $8$ rows, but it is clearly suboptimal as there is a tree at the bottom which is not doing enough work.


 * Dudeney-Modern-Puzzles-149.png