But he spent

         most of his time

             looking at plants and fungi.

     The cells of plants

         and fungi

              have cell walls.

     This makes them

         easy to see.

     Animal cells

         do not have cell walls.

     This absence of cell walls

          makes it harder

               to see the outline

                    of animal cells.

     Because Hooke

          couldn't see their cells,

        he thought

             that animals

                 weren't made of cells.