the mean temperature of the same period, the products do not deviate widely from one another in the same species. It was thereupon assumed that these deviations are due to incorrect observation, and that such a constant product of the period of vegetation and the mean temperature will be found in every species. This product then received the unmeaning appellation of the sum of the temperature. If such a relation between vegetation and temperature really exists, it would necessarily follow that other things, such as light, moisture, the soil, &c., have no influence at all on the period of vegetation, not to speak of those internal causes which help to complicate the simplest processes of growth. It is unnecessary to expose in this place the absurdities involved in this idea of the sum of the temperature; the needful remarks will be found in the 'Jahrbücher für wissenschaftliche Botanik' of 1860, i. p. 370. It is a remarkable fact however that such monstrous reasoning should have been able to prejudice science in various ways even later than the year 1860. A new science was actually invented and called Phaenology, which accumulated thousands and thousands of figures, in order to discover the sum of the temperature for every plant, and as this crude empiricism showed that the simple multiplication of the period of vegetation by the temperature gave no constant result, the square of the temperature was tried and other tricks of arithmetic adopted. Though Alphonse de Candolle as early as 1850 expressed well-founded objections to the whole of this method of treating the subject, in which the mean temperature played much too important a part, yet he was so far unable to keep clear of the prevailing ideas, that he thought he could express the effect of light by an equivalent number of degrees of temperature, and so save the supposed law of temperature in vegetation. To this idea may be traced his work on the geography of plants, published in two volumes in 1855, which however contains a rich treasure of personal experience and knowledge of the works of other writers.
