Definition: A depression caused by erosion by water or ice. Low-lying land bordered by higher ground; especially elongate, relatively large gently sloping depressions of the Earth's surface, commonly situated between two mountains or between ranges of hills or mountains, and often containing a stream with an outlet.
Definition: veins run parallel and equidistant to each other for most of the length of the leaf; they may converge or fuse (anastomose) towards the apex
