With this paper the author concludes a series of studies he began in 1941; the work deals with a cupuliform organ, with hairy margins, located in the junction of radicle and hypocotyl of seedlings of 105 species of Eucalyptus. It was found out that in the embryo the organ looks like a ring placed on the end of the hypocotyl; for this reason one my led to consider the organ at this stage as merely a thickening of the radicle's end; however the radicle can be seen as it comes out from the center of the organ in discussion. Shape, size the diameter of the "mouth" of the organ as well as its hairs vary with the species under consideration. As far the anatomy of the organ is concerned it shows a cortical parenchyme covered on both faces, by the same epidermis with covers the hypocotyl; this epidermis extends itself till the radicle. The hairs are generated in the margin of the organ. The ecological significancy of the dome-like organ is rather obvious. It permits to the seedling to get into close contact with the soil long before the radicle becomes enough large to carry on its own functions. By this way there is no lack of continuity in the physiology of the nutrition which is of a great importance to the seedlings since the seeds from Eucalyptus are exalbuminous. Since the cupuliform organ constantly appears in the seedlings of the 105 species studied by the author, one can safely establish ic as a characteristic of the genus Eucalyptus occurring only at the seedling stage. Further studies are now being conducted to verify whether the cupuliform organ occurs in other genera of the Myrtaceae family or not.