The causes underlying the initiation of the spring diatom flowering have been a subject of vigorous discussion in recent years. With the gradual accumulation of records it has become quite clear that no one factor controls this peculiar phenomenon. The obvious prerequisite, an abundant supply of nutrient salts in the euphotic zone, is generally satisfied during the autumn and early winter, yet a flowering does not in most cases follow immediately. In a few localities, such as Cape Cod Bay and Ipswich Bay (Bigelow 1926), the Woods Hole region (Fish 1925), and Long Island Sound (Riley 1941a), diatom bursts have been recorded in December or January, but in most north temperate waters they do not occur until March or April...