For instance, the difference between the long-stalked and finely-cut leaves of Anemone attacked with rust and the normal leaves with broad segments, or between the urceolate leaves occasionally found on cabbages and the ordinary formin these cases undoubtedly pathological and teratological respectivelyis nothing like so great as between the upper and lower normalleaves of many Umhelliferae or the submerged and floating leaves of an aquatic Ranunculus or Cabomba.
Useful and suggestive as they often are, teratological facts played, at one time, too large a part in the framing of morphological theories; for it was thought that the monstrous form gave a clue to the essential nature of the organ assuming it.
Roots are often flattened, twisted and otherwise distorted by mechanical obstacles; stems by excess of food in rich soils, the attacks of minute parasites, overgrowth by climbing plants, &c. Leaves are especially apt to vary, and although the formation of crests, pitchers, puckers, &c., must be put down to the results of abnormal development, it is often difficult to draw the line between teratological and merely varietal phenomena.