Developmental History of the Abnormal Structure in the Geophilous Organ of <i>Aconitum</i>

Abstract

1. The abnormal structure found in the root-tuber of Aconitum mitakense NAKAI has been described. This species is one of the representatives which exhibit the most remarkable abnormality, the tuber having both the very sinuous cambium and several separate strands of cambium. The remarkable abnormality of cambium is usually found in the tuber more than 2cm. in diameter.2. The development of the tuber has been traced. Under cultivation, the daughter tuber begins to appear in March, before the erect stem comes to sprout. In that time it is very small, 1.5mm. in diameter, but in the middle of April it thickens to one third of the mother tuber in diameter, and at the end of the month, to nearly one helf of it.3. The developmental history of the abnormal cambium has been traced. In the earliest stage of development, a circular zone of meristematic tissue appears in the part inside the primary phloem and outside the primary xylem, though the tangential row of initial cells is not evident. Next some fragments of the tangential cambium appear in the zone. Soon later the pith begins to change into meristem, from which secondary phloem strands and fragments of the secondary cambium are differentiated. By the connection of these fragmental rows of cambium, the sinuous or separate cambial features, found in the full-grown tuber, are produced.4. For comparison, the abnormal structure in the geophilous organ of Aconitum gigas LÉV. et VAN. (a species of Lycoctonum) has been examined.5. The relationship between the two sections of Aconitum, i.e. Lycoctonum and Napellus, has been considered. In Lycoctonum, the geophilous organ, which exhibits the abnormal structure, is represented by the perennial rhizome, while in Napellus by the biennial root. Further their abnormalities are also fundamentally different from each other in the developmental process and in the histological characters. From these facts, it is quite unreasonable to assume that the one represents a more original type than the other; and the phyletic gap between Lycoctonum and Napellus seems to the writer to be fairly large.