Trees Aren't Synchronized

I am ready now for all the trees to be green. Along Indian Hill Boulevard, first the grey-trunked sycamores leafed out, leaving the white-trunked ones bare. Then, a couple of weeks later, the white-trunked ones followed suit. The big elms farther down the boulevard came out in reddish buds and got all sexy, dripping flower parts all over the sidewalks and streets. Another street I drive along on the way to work has a few trees that still have no leaves at all. Several have gone through their redbuds or white drifts of flowers and leafed out. But still the two or three bare trees remain without leaves. I wonder each morning, will I see green or will I keep hoping in vain? Are they dead or just very sleepy?