Rankness affords another example where superfluity of water is concerned, though it does not involve simply this, because the plant may also contain excessive quantities of nitrogenous and mineral matters taken up by the roots.
Rankness is, in fact, in many respects analogous to etiolation in so far as the tissues are soft and surcharged with water, but it differs fundamentally in the deep green of the chlorophyll: this may lead to abundant assimilation if free access of air and drier conditions can be gradually brought about. Any sudden drying, however, may be fatal to the tender tissues.
Rankness commonly depends on excess of food materials, especially nitrogenous manures, as may be seen in meadows and cornfields where the manure heaps have remained on the ground and saturated it to excess as compared with the rest of the soil; this may often be observed with weeds, etc., in the neighbourhood of farm buildings. If the period of rank growth is accompanied and followed by days of suitably bright sunshine and dry air, the increase of vegetative structures usually results in increased flowering, heavy crops, or strong wood; but if the rankness continues too long, or is accompanied by wet and dull weather, the watery tissues are peculiarly susceptible to attacks of fungi and insects, and to damage by sudden frosts or chilly winds. Rankness affords, in fact, a typical illustration of predisposition to disease.