The riddle of the grass

Spring meadows are full of riddles: 

“In cocksfoot and many other species, the leaves emerge pointing vertically upwards. How do the grasses manage to bring their leaves elegantly and intactly into the horizontal position? Answer: they incorporate a joint. This is probably already laid down when the leaf is forming in the stalk. But how do the cells of the joint differ from the other leaf cells? Are they larger? Smaller? Do they swell more than the other leaf cells? Perhaps a microscopic examination could provide clarity here.”