More leaf windows

It’s a sunny Saturday morning, and one regular chore is watering the house plants.  The sunlight was hitting a nice little Haworthia, a succulent member of the lily family (although recent phylogenetic shakeups may have changed that), and the leaf windows were pretty obvious.  They tend to look darker green, but you're really looking down through the leaf tissue.  Thick leaves are good for conserving water, but their very thickness means light penetration is limited.  Having transparent areas on the upper ends of their leaves not only allows light to penetrate deep into the leaf, but it also allows a plant like this to grow almost buried in soil.  Keep your eye out for similar features on other thick-leaved plants, you can never guess where they might appear.  And of course TPP's usual reminder; being a succulent is not the same as being a cactus.  The former is an adaptation for xeric environments that you can find in many groups of plants.  Cacti are a specific family of plants.