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with regard to wheat in America after an extensive research, but within the past few years much more åttention has been given to this subject.

The differences between the quantities of heat required in England and America and the differences in the varieties of the wheat were apparent to Lippincott. Thus, he finds that in England the lengths of the periods and the sums of the temperatures were as follows: In 1860 a period of 59 days and a sum of 3,562° F.; in 1861 a period of 50 days and a sum of 3,225° F.; in 1862 a period of 56 days and a sum of 3,406° F. The reduction of the mean temperature during two months of 1853 by merely 2° F. cut off one-third of the crop and brought a famine that was already foreseen in July, 1853. On the other hand, it increased the exportation of wheat and flour from the United States from $14,000,000 in 1852 and $19,000,000 in 1853 to $49,000,000 in 1854.

A careful study of the sum totals of rainfall, temperature, and sunshine should enable one, in general, to foresee similar failures and corresponding successes in the crops of any region.

QUETELET.

The suggestive, but sketchy, studies of earlier writers on thermal constants were supplemented by more elaborate investigations and calculations of statistics by Quetelet (1849) in his Climate of Belgium, from his own summary (p. 62), etc., I take the following

notes:

for

The details hitherto given show sufficiently that the relative conditions of vegetation change at all times of the year in two countries situated at a distance from each other. Acceleration and retardation are quantities essentially variable, and it is erroneous to say that one locality has its budding period ten or twenty days sooner, example, than another. This difference may be correct for one season of the year and entirely wrong for another; and, moreover, we can only pretend to state a fact which applies to the majority of plants.

Nevertheless the differences in the periods of budding are not so variable but that we can assign to them values very useful to consult in practice. On the other hand, science needs to establish some welldetermined facts in order to arrive later at the knowledge of the laws upon which these variations depend. I believe that in the actual state of things I shall be able to settle upon the following epochs, in order not to multiply too much the terms of comparison. Moreover, the numerical tables justify, to a certain extent, the distinctions which I lay down.

Let us first observe that the awakening of the plants is brought about by the cessation of the cold, and it suffices to consult the tables of temperatures for the different countries to determine the average epoch at which many plants will put out their leaves or their flowers. These first indications, which it is well to collect, still do not determine, however, the general movement of vegetation which may

manifest itself more or less slowly. They are given by the budding of the Galantus nivalis, of the Crocus vernus, by the appearance of the catkins of the Corylus avellana, of the leaves of the Ribes grossularia, of the Sambucus nigra, of the honeysuckle, and of some spireas. The falling of the leaves is also determined by the temperature, and in our climate generally takes place after the first frosts. This period and that previously mentioned come ordinarily at the two Îimits of winter, and they separate to make place for the different stages of vegetation in proportion as the cold of winter has a less duration. The winter sleep lasts in our climate from three to four months; in southern countries it is very much shorter. We can even imagine a line on the surface of the globe where it ceases altogether for the generality of plants."

The great movement of vegetation commences in Belgium in the middle of March and terminates at the end of April. I will call this the period of leafing (feuillaison), because during this interval the different plants are covered with their verdure and some of them show their first flowers.

The second period is that of flowering (floraison), which in our climate would include the months of May and June and the first half of July.

The third period would then come, which is that of ripening (fructification).

These three great periods should undoubtedly be in their turn subdivided, but the present state of the observations does not allow of such detail. It is understood, moreover, that the names I have given to them only serve to designate the principal phases of vegetation which take place. Thus, in making the general table [omitted-C. A.] I have classed the different plants according to the following seasons:

Awakening of the plants. This period is determined by the plants comprised in the [omitted] table.

Leafing. This period comprises the plants which, in Brussels, put out their leaves from the 15th of March to the 30th of April, and which bud during the same two months.

Flowering. I have made use of the plants which have flowered or brought forth their fruit from the 1st of May to the 15th of July.

a As I have already observed elsewhere, the awakening is an epoch that is not the same for all plants. I mean to speak here only of the epoch when the sap begins to circulate in the majority of the plants which grow in our climate. "All plants do not begin to vegetate at the same period," says M. Ch. Martins, in the Botanical Expedition along the Northern Coasts of Norway. "Thus in some the sap begins to mount when the thermometer is only a few degrees above zero (centigrade); others need 10 or 12 degrees of heat, while those in warm climates require a temperature of from 15° to 20° C. In a word, every plant has its own thermometric scale, whose zero corresponds with the minimum temperature at which vegetation is possible for it. Consequently, when we wish to determine the sum total of the temperature that has determined the date of flowering (fleuraison) of each of these plants it is logical to only consider for each plant the sum of the degrees of temperature above zero (centigrade), since these temperatures are the only ones that have been efficient in inducing or sustaining their growth." In tropical countries the great fluctuations in the vegetable kingcom are not regulated by the same meteorological elements as are effective with us; there the rainy season produces very nearly the same effects as the cold season does in our climates.

Ripening. This period comprises the stage of vegetation, which, for Brussels, extends from the 15th of July to the falling of the leaves, the last limit of the period with which we are occupied here.

This classification has allowed me to put into [the omitted] table the observations gathered from other sources, as well as from the system of comparative observations which the Royal Academy of Belgium has succeeded in establishing at Brussels.

The average influence of location on the annual progress of vegetation.

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This table of average intervals shows how variable is the acceleration of one place over another during the different seasons of the year. This acceleration even often changes into retardation, consequently the isanthesic lines are far from remaining parallel. We therefore conclude that latitudes and longitudes are not the only and principal causes which regulate the phenomena that are engaging our attention, because these unchangeable causes could not produce different effects; it is the same with regard to altitudes, we must only consider them as intermediary agents, and we should do wrong to take them as the basis of calculations for determining the epochs of natural phenomena. Let us see whether temperatures will give more satisfactory results. In order to facilitate the comparison I have gathered in the table (which unfortunately has not been completed for all the localities) the average temperatures for years, seasons, and months.c I must limit myself to consulting these elements, as I have not the necessary data to compute the base of daily temperatures and particularly to take the action of the sun into consideration. This first work will perhaps make us feel the incompleteness of the system of meteorological observations adopted at present (1849) in Europe. I have also been obliged to exclude the influence of the temperature of the earth, although it is absolutely necessary to consider it, in order to treat, the phenomena of vegetation in a complete manner.

b

The mean temperature in winter at Brussels is 2° C. The most favored localities in comparison with it are Naples, Alais, and Polperro (near Lands End, England). I have not been able to deter

a It will be understood that I wish here to speak only of the action of geographical circumstances considered outside of the influence of temperature. This action has been but little studied up to the present time, but it is well worthy of our consideration. The following is what one of the most distinguished living botanists of the present time has written to me on this subject: "The distribution and extension of each species of plant over the earth shows us that the plants in general and each species as a unit are subject to organic changes dependent upon longitude and latitude. Each has a limited range; between these boundaries it has its paradise, where it thrives best. The organic changes which take place in individual plants, if one compares those that are native in different places, are such that we might presume that even their periodic phenomena must be affected. For example, all plants are stunted in height and in the number of their leaves toward their northern limit (or rather polar limit). They change their general appearance in going from east to west on the same parallel; they alter as to the extent of inflorescence and the size of flowers in going north or south on the same meridian. Now, as it is only by means of these organs that the plant vegetates in the presence of the world outside of it, it is necessary in our observations to begin with the relation of those organs, or rather the consideration of the developed organs ought to enter into our notation of their vital action. It further follows from this that we ought to study plants whose natural boundaries are known to us; these are the true barometers for vegetable life" [i. e., as the barometer is the measure of the activity of the atmospheric forces, so the natural geographic boundaries are the measures of the vital activity of plant life]. (Letter of M. de Martin's Observation of periodic phenomena, Mem. Acad. Royal," Brussels, Vol. XVI, p. 11.)

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Further, it has sometimes been necessary to give the temperature of a neighboring locality instead of that of the place itself; thus for the temperature of Polperro I have taken that of Penzance, and the temperature of Makerstoun has been replaced by that of Edinburgh, etc.

c I have omitted these figures in my copy of Quetelet's table.-C. A.

d I should have liked to supplement this work with maps showing the principal epochs in vegetation, but the collected observations are not yet sufficiently

mine the epoch of the awakening of the plants in the first two places, but in the last mentioned the acceleration is forty-one days. This acceleration is also very great at the other stations of England, as well as at Valogne, which has also probably a sea temperature.

It has also been impossible for me to fix the time of awakening for places where the winter is the most rigorous, such as Lapland, Sweden, and the United States. We have seen, however, that there is twenty days retardation in places where the mean temperature is very little below zero. Jever seems to be an exception to this rule; but the results obtained in this place were only deduced from three observations.

The epoch of leafing corresponds, as we have said, with the end of March and the month of April, and that of the flowering with the months of May and June. The first includes the commencement of spring, the other the end of it. Thus the temperature of Brussels in spring is 10° C. The greatest variations besides are at Naples and at Alais. It is also in these places that the leafing takes place first. Venice, Parma, and Guastala are very little in advance, but the month of March and the beginning of April are scarcely any warmer than at Brussels. The difference of temperature is only felt in a marked manner in the following months. The flowering also takes place about eighteen days sooner.

Polperro, in regard to leafing, is about ten days in advance. The temperature in March is much higher than that of Brussels, while in April it is about the same. The advantage is lost in the following months, when, as regards flowering, Brussels is in advance of Polperro, as well as of the localities in England.

Brussels is about eighteen to twenty days ahead of the towns of Holland and Germany in the epoch of leafing, and is behind in the

complete to allow of undertaking such a task. The first chart would have shown by a series of lines drawn over Europe the awakening of plants for each ten days, that is to say, a first line would indicate the localities where the awakening first takes place immediately after the coldest day of the year, which with us is about the 20th of January; a second line would pass through places where the awakening is on an average ten days later, and so on. Another system of similar lines traced upon a second chart would have indicated in the same way the beginning of budding, always proceeding by intervals of ten days. We should also have made similar charts for flowering and ripening and the fall of the leaves. By comparing these charts we should be able to see at a glance the principal changes which take place in these various systems of lines. order to complete this study we should imagine other systems of lines relating to temperatures. Thus one system would show the localities in Europe where frosts first cease, always advancing at intervals of ten days; then another system for places which, at successive intervals of ten days, and beginning from the awakening of the plants, have reached a sum total of temperatures amounting to 183° C., corresponding to the epoch of leafing; further, a third system of lines which should pass through places that, counting from the time of awakening, have successively attained the total number of degrees of temperature necessary for the flowering of plants; and so on for further systems.

In

The charts relating to vegetation and those relative to temperatures would, by comparing them, give much curious information. Unfortunately the observations we possess of daily temperatures are still as rare as those of the flowering. I have therefore been compelled to renounce that portion of my work.

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