ADVENTITIOUS (from Lat. adventicius, coming from abroad), a quality from outside, in no sense part of the substance or circumstance: a man's clothes, or condition of life, his wealth or his poverty, are called by Carlyle "adventitious wrappages," as being extrinsic, superadded and not a natural part of him. In botany the word means that which is not normal to the plant, which appears irregularly and accidentally, e.g. buds or roots out of place, or strange spots and streaks not native to the flower.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)