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

Modern Puzzles by Henry Ernest Dudeney: $149$

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.

Sources

• 1926: Henry Ernest Dudeney: Modern Puzzles ... (previous) ... (next): Geometrical Problems: Various Geometrical Puzzles: $149$. -- A Tree-Planting Puzzle
• 1968: Henry Ernest Dudeney: 536 Puzzles & Curious Problems ... (previous) ... (next): Combinatorial & Topological Problems: Point Alignment Puzzles: $435$. A Tree-Planting Puzzle