THE GROWTH‐FORMS OF THE FLORA OF NEW YORK AND VICINITY

There has recently appeared in a work on the flora of New York,2 an account of the relation between climate and the vegetation in which the length of the growing season was used as the chief temperature factor. This was done for the reason that it seemed to account for the distribution of the flora more closely than any other ascertainable temperature factor. While it is difficult to conceive of any climatic agency, such as the number of frostless days, the maximum or minimum temperatures, or the accumulated heat units, as actually controlling the distribution of the flora, yet it is a matter of common observation that temperature does affect vegetation and its distribution. How, then, are we to measure the effect of climate, and particularly temperature, on plant life? All of the older methods, including the one used in the flora of the vicinity of New York, have studied climate as a rather distinct entity, and then imposed a somewhat rigid, usually instrumentally correct scheme, on a complex aggregate like a local flora. All such schemes require considerable wrenching of the purely climatic factors on the one hand, as they certainly do of the assumed vegetative response on the other. Until recently, and with the possible exception of Merriam's "Life Zones," all studies of the effect of temperature on plants were of this type. They were essentially attempts to explain the facts of plant distribution by measured temperatures or heat units or frostless days or by some combination of these methods. Raunkiaer3 has studied temperature factors from an entirely different vi2wpoint. His idea, briefly, is that we must study climate,