Complex sentence: The scars, or leaf cushions, were composed of green photosynthetic tissue, evidenced by the cuticle covering and being dotted with stomata, microscopic pores through which carbon dioxide from the air diffuses into plants.
Split into simpler sentences: The scars, or leaf cushions, were composed of green, photosynthetic tissue. This is known because each is covered by a cuticle and is dotted with stomata, microscopic pores through which carbon dioxide from the air diffuses into plants.