I wouldn't bother about loops, they are allowed if you're not graphing functions[1] and are quite common on (x1/x2) graphs as opposed to (x/t) graphs.
My real issue with it are unlabeled axis - without them those graphs have no meaning except as an conceptual illustration of an idea that something loops around while growing. Also, OP assumed that x is time, which it does not have to be for the "graphs" to make sense.
My real issue with it are unlabeled axis - without them those graphs have no meaning except as an conceptual illustration of an idea that something loops around while growing. Also, OP assumed that x is time, which it does not have to be for the "graphs" to make sense.
[1] - see e.g.: http://en.wikipedia.org/wiki/Phase_space
tl; dt: nitpicking, and also picking the wrong nit.