flowering season, particularly as regards Prague, where the temperature in April, May, and June is a little higher than that of Brussels. The retardation for stations in Sweden, the United States, and Lapland is sufficiently explained by an examination of the temperature tables, and also in regard to the epoch of ripening (fructification).

I have already had occasion to call attention elsewhere to the fact that the falling of the leaves (effeuillaison) depends less upon the temperature of the year than upon the effects of the first cold. Thus the leaves fall sooner in the north than in the south, unless they fall sooner here on account of a season of great dryness or excessive heat. It would be superfluous to consider the influence of the other meteorological agents when we still possess so little information as to the mode of action of the principal cause, which, in our climate, dominates in some degree all the phenomena of vegetation.

The temperature month by month at Geneva and Lausanne vary little from that observed at Brussels. The winter months there are a little colder and the vegetation is a little behind. Toward the time of ripening this retardation changes into an advance. The temperature, however, in spring and winter is no higher than that of Brussels.

Is not this advantage to be attributed to the fact that Geneva and Lausanne, having a higher elevation, enjoy purer air and a more efficient solar radiation, elements which are not indicated by the thermometer? By following the mode of calculation generally adopted one would say that the difference of latitude between Brussels and the two Swiss cities is compensated by their different altitudes. Geneva and Lausanne are 4° 30' farther south than Brussels, while their elevation averages about 420 meters greater, which shows that a degree of latitude farther north is about equal to an increase in height of 120 meters. At Munich and Gröningen the same plants flower almost simultaneously, yet their latitudes and elevations are very different. Munich is 5° 4' farther south, but is 524 meters higher. Here again a degree of south latitude nearly compensates 100 meters of elevation. It is to be regretted that we do not know the annual temperature of Gröningen. Berlin and Stettin seem to approach that locality very nearly in the natural epochs of their plants. Indeed there is very little difference in their latitudes, their elevations, and probably, also, in their temperatures.

Carlsruhe and Brussels have about the same annual temperature. The winter and early spring are a little colder in the first than in the second of these cities, consequently the vegetation is a little later; on the other hand the months of April and May are warmer, therefore, we see the vegetation changes its retardation into an advance.

Carlsruhe is about 2 degeees south of Brussels. For this reason alone vegetation should be about eight days in advance as at Paris; but on the other hand its altitude is about 300 meters greater than that of Brussels, and its vegetation should for this reason be about twelve days later. Combining the effects of these two causes, Carlsruhe would still have a retardation of more than four days, which is confirmed by experience for the first portion of the year; but in the second part we see this retardation change to an advance of fifteen days. Should we not here again remark, as was done before, that,

other things being equal, vegetation is much more active on high plateaus, where the radiation is greater, as well as in localities where the annual variations are very marked? This activity is further reenforced if the locality is near the polar regions, where the light acts almost uninterruptedly when once the awakening of the plants has taken place. In this respect Russia and Lapland present us with notable examples of this reënforcement.

Kupffer, in his "Note relating to the temperature of the soil and of the air at the limits of the region of cultivation of cereals," gives the following temperatures for the three principal boundary points of this region:

"A comparison of the curves for Nertchinsk, Irkutsk, and Archangel demonstrates in a striking manner," says Kupffer, "under what climatic conditions the cultivation of cereals can be carried on notwithstanding the lowness of the average annual temperature. All the curves agree together in spring and autumn, whence it results that it is especially the temperature of spring and autumn which influences the cultivation of cereals; it is in these seasons, in fact, that occur the two most important periods of the year for agriculture the time of sowing and the time of reaping. In the cultivation of rye autumn plays a still more important part, because rye is sowed also in autumn." Kupffer calls attention in another part of his note to the fact that some kinds of farming are carried on where the soil below the surface is frozen. "Experiments in farming," he says, "have been made at Irkutsk, on a very small scale it is true, but which in many respects have been a success. due to the fact that the soil becomes soft on the surface and is thus capable of developing the germs received by it; its mean temperature is above zero four months in the year, which is sufficient to ripen the cereals in a country where continuity of the sunshine makes up for the weakness of solar action. Snow often falls upon the sheaves, but still they harvest them." These examples confirm what we have said in regard to annual changes of temperature. In no locality in the world are these variations greater than here; at Yakutsk the difference of temperature between the warmest and the coldest month of the year is 50.9° C.; at Irkutsk, it is 24°.1; at Nertchinsk, 39.°1; at Archangel, 28.2° C.

This is

It might be said, it is true, that the average temperature of the year should not be considered here, not even that of the free air, so long as the plants are covered by snow to shield them, for in this case the temperature of the air does not at all represent that of the plants. In this respect the conditions of vegetation would be the same at each

locality about the time of the winter awakening, and we should particularly consider the temperature that follows after the thermometer has passed the freezing point, as well as the quantity of light radiated by the sun.

It must therefore be admitted that cold, as long as it does not destroy the life of the plant, may be more or less severe or more or less prolonged, and thus lower the average yearly temperature, without causing any marked difference in the epochs of vegetation. This reflection explains, independent of all hypothesis, that for any equable mean annual temperature the acceleration in vegetation should be in favor of localities where the annual variation is the greatest, particularly in northern countries, where the frost prevails during many months of the year and where duing many of the following months the sunlight never ceases to fill the sky. Admitting the hypothesis that the action is proportional to the sum of the squares of the temperatures, the results are still more positive; for, other things being equal, the greater the annual variation the greater will be the sum of the square of the positive ordinates in the curves of temperatures.

I will now present some conclusions that one can deduce from all that precedes. I must first of all warn my readers that this work must be considered only as an attempt to solve a problem as difficult as it is interesting, the principal elements for the solution of which are still wanting.

1. A great number of factors combine to produce variations in the periodic phenomena of vegetation, the most important of which in our climate is temperature.

2. It may be estimated that the progress of vegetation is in proportion to the sum of the temperatures, or, better, to the sum of the squares of temperatures, calculated above the freezing point, starting with the epoch of the awakening of vegetation after the winter sleep. 3. The cold of winter, if it does not injure the vitality of the plant, does not cause any perceptible retardation in its future development, particularly if the ground has been covered with snow.

The effects that can be produced by the cold of winter must, however, be considered, and especially the condition of the plant when it entered upon its winter sleep, a condition which should correspond to a certain sum of acquired temperatures (or heat stored up). As to the ripening of the harvest and because plants develop under the influence of the sun, we must consult a thermometer exposed to its direct action, and not a thermometer exposed to its direct action, and not a thermometer placed in the shade, as is commonly done.

4. The temperatures at night are not comparable with those of the day as to their effects on vegetation. The quantity of light received by the plants must also be taken into consideration.

5. An increase of 1° in latitude produces about the same retardation in vegetation as an increase in elevation of 100 meters; that is to say, in our climate, a retardation of about four days.

This result should be looked upon as only a kind of average of quantities that vary during the year, the differences of latitude and elevation having scarcely any real influence further than as they produce differences of temperature.

6. The variations of temperature, other things being equal, are

favorable to vegetation, and the same may be said of high plateaus where radiation is more powerful.

7. The isanthesic lines, or lines of simultaneous flowering, do not preserve any parallelism at different periods of the year; thus, the line which shows where the lilac blooms on a given day of the month passes ten days afterwards through another series of places where the same phenomena is then occurring.

Now, the zone comprised between these two lines has not the same breadth throughout its whole extent, as would be the case with a zone between two parallels of latitude. It is not even constant, since, for example, a month later the isanthesic lines will have quite different forms, and localities that were backward as compared with others may then be in advance.

8. The falling of the leaves is a phenomenon which in our climate depends as much upon the current temperature as upon those which have preceded. It is generally controlled by the first cold of autumn.

FRITSCH.

Karl Fritsch (1881) gives the results of about ten years' observations of plants growing in the Botanical Garden at Vienna (1852– 1861). His list of plants embraced all those recorded in the previous lists of Quetelet, Sendtner (1851), and his own, in all 1,600 species and varieties, but of which he has only used 889. The epochs observed by him, as uniformly as possible throughout the ten years, were the following:

(1) The first visibility of the upper surface of the leaf.

(2) The complete development of the first flower.

(3) The complete ripening of the first fruit.

(4) The date at which a tree or bush has lost all of its foliage. Having endeavored in vain to establish a connection between the moisture of the air and the growth of the plant, and finding it impracticable to take account of the moisture in the earth, Fritsch resolved to reject observations made during special droughts or floods or other abnormal conditions and to consider only the sum of the average daily temperatures. These mean daily temperatures he deduced from the observations at 6 a. m. and 2 and 10 p. m., made at the Central Meteorological Institution in Vienna, where the thermometer was about 50 feet above the ground. The summation of the mean daily temperatures for comparison with phenological phenomena counts from the 1st of January to the date of the observed epoch, and omits all days whose mean temperatures are 0° Réaumur or lower than that. A comparison of the observations made on successive years on the same plant shows that the time of blossoming is uncertain by only one or two days in 96 per cent of all the plants, and the so-called "temperature or thermal constant " is uncertain by 3 per cent of its amount or less, in 97 per cent of all the plants. Similarly, for dates of ripen

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ing of fruits the dates of ripening as predicted by the temperature constants have an uncertainty of one or two days only in 94 per cent of the cases. In the choice of the date from which to begin taking the sum of the mean daily temperatures, it would seem that for annual plants the date of sowing the seed would be proper, but that for perennial plants the whole winter since the end of the preceding growing season would be proper; but instead of the latter, Fritsch has adopted that epoch at which the mean temperature of the day has its minimum value in the course of its annual variation, and this, combined with the ease of computation, leads him to adopt the 1st of January for all perennials. For the biennials and the annuals he would have preferred to count from the time of sowing the seed, but as the latter date was frequently not recorded and as most of the temperatures are below freezing in the early part of the year, he finds no large error introduced by adopting the 1st of January for these also, and this is very nearly equivalent to Quetelet's method of counting from the time of the permanent awakening of the activity of the plant in the spring.

In the following list I have given all of Fritsch's results, and with reference to the practical application of these figures to the prediction of similar phenomena elsewhere quote his statement that he had convinced himself in many ways that the trees and shrubs observed by him in the Botanical Gardens at Vienna blossomed at the same time as those in the open country, but for all herbs this is true to a less extent, and only in a few cases are the departures important.

Although many plants do not ripen in the short season at Vienna, yet he was able to determine their thermal constants for the date of blossoming.

In general the plants and their seed had by long cultivation in Vienna become acclimated to that locality, so that by applying Linsser's theorems to Fritsch's results they become applicable to the phenomena that would be manifested by these plants in other parts of the world.

As concerns the temperature of the soil, Fritsch states that the perennial grasses were partly shaded by trees until 1852, after which they were cultivated in a sunny spot. The annual grasses were uniformly in a sunny region, slightly inclined toward the north.

The orders or families, with the genera and species and sometimes varieties included within them, are arranged in the table as given by Fritsch, who states that it is in accordance with the natural system of Endlicher, which is generally adopted in Austria as preferable to a chronological or alphabetical. But for the convenience of American readers I have added to each of Fritsch's orders the number by which it is designated on pages 5 and 736 of Gray's Manual of