This contribution is a detailed refutation of the Age-and-Area hypothesis of J. C. Willis. Rate of dispersal of plants shows that the present flora covering the vast glaciated area of N. America has occupied it in a few thousands, instead of millions, of years; and has reached a tolerable equilibrium. Willis'' ideas are derived from often antiquated and usually inaccurate printed data or from misleading herbarium material. Examination of the list of cosmopolitan species in the New Zealand flora as given by Willis shows that their determination is exactly 100% erroneous. The conclusion that large genera are old and small genera are young is not borne out by the facts. The following large genera are young Eriogonum, Lupinus, Oenothera, Phacelia, Dianthus, Silene, Verbascum, Centaurea, Hieracium. Large genera as Crataegus and Rubus, which may be fairly old, occur chiefly in regions which are geologically young and which were hence available for occupation in late Tertiary or even in post-glacial times; on the other hand, small genera like Podophyllum, Panax, Epigaea, Liriodendron, Nelumbo, Sassafras, etc., can frequently be demonstrated to be old.