mother plant down to the seed produced by it. Therefore in every kernel of seed there is concealed the whole relation between the development of the plant and the total heat of the locality where it was produced. Two seeds of the same species, one of which comes from a mother plant that has lived under the influence of an annual total heat of M, but the other of which comes from another mother plant that has lived under a total annual heat of N, possess powers of development, or a sensitiveness to equal temperature influences, that are inversely proportional to the sums M and N; or, in other words. the rate of development is equal to the sum of the effective temperatures divided by the normal values of the total annual sums for the mother plant.

Applying this law to seeds that are artificially transported from their homes to other places having different climates as to temperature we are enabled to predict approximately what their behavior will be. Thus Von Baer observed that cress seeds that had been raised in St. Petersburg (lat. 60°) and transported to MatotschkinSchar (lat. 73°) developed in July at only one-third the rate that they did in St. Petersburg in the month of May. Now the annual sum of positive temperatures for St. Petersburg is 2,253° C., and the average temperature of the month of May in St. Petersburg is 11.2°, while that of the month of July at Matotschkin-Schar is 4.4°. Therefore the rates of development per day of the same seed at these two places will be in the ratio of 11.2 to 4.4, or 2.6 to 1. Again, for cress seeds raised at Matotschkin-Schar, where the annual total heat is 330° C., the rate of development will in general be 2253, or 6.8 times more rapid than the development of seeds brought from St. Petersburg. Vice versa, seeds carried from Matotschkin-Schar to St. Petersburg the rate of development will be 6.8 times more rapid than for those that are native to the latter climate.

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Linsser was thus able to enunciate the first step in the rational explanation of a phenomenon with which agriculturists had long been familiar-viz, that the seeds raised in northern zones retain the power of rapid development, so that when sown in southern regions they grow more rapidly and ripen earlier and give a richer harvest than those that are sown in their native warm locality. Similarly, seeds of mountain plants, when carried by rivers into the warmer plains of the lowlands, develop plants whose blossoms antedate the spring blossoms of the plants native to the lowlands. We may thus accept the general statement that plants or seeds transported to colder countries reach a given stage of vegetation later than the

A beautiful illustration of this law is found in the abnormal early flowering of seeds brought from the cold uplands and lodging on High Island, on the Potomac, about 5 miles above Washington, D. C.

native plants, but when transported to warmer regions they blossom and ripen earlier. Thus in 1859 Schuebeler sowed 6-rowed barley that had been raised in Alten (lat. 70° N.), where it required only nine weeks to ripen, in Christiania (lat. 60° N.), where it ripened in eight weeks. In the same year some of the same barley was carried from Breslau, where it required nine and a half weeks, to Christiania, where it ripened in twelve to fourteen weeks. Linsser arranged these experiences as shown in the following table, in which he assumes that both at Alten and at Christiania the barley is sown when the mean daily temperature is about 8° C.

The annual sum totals of heat are 1,300 in Alten and 2,600 in Christiania. Therefore we see that the heat required by seed acclimatized at Alten (700) is to that required by seed acclimatized at Christiania (1,400) in the same ratio as the annual sum totals.

It can also be shown that barley acclimatized at Christiania and transported directly to Alten can not ripen in the latter place, since the 1,400° C. required by it at Christiania are not received at Alten. It is only by gradual progressive acclimatization at numerous intermediate places that the plant has been enabled to adapt itself to successively smaller sum totals of heat. In continuation of this process the barley that is now accustomed to ripen at Alten can be used to pioneer the further northward progress of its species. The attempt to transport barley from Denmark to Iceland has thus far failed, but doubtless barley from Alten would succeed. Barley cultivated in the Caucasus at an elevation of 7.000 feet and transported to St. Petersburg should, according to Linsser's computation, experience an acceleration, so far as climate is concerned, as though it were coming to a warmer climate, but this acceleration may be more than counterbalanced by the differences in the nature of the two species of plants, as it is well known that the Turkish oats (1vena orientalis) require more time to ripen than the ordinary oats of northern Europe; the variations in times required by different kinds of oats, barley, and wheat, and even winter rye, are oftentimes larger than the variations due to differences of climate. But such variations, as observed in plants that are only partially acclimatized, will disappear after a few generations if the plant has the power of adapting its internal organ

ization to a new climate. The geographical limits of any species, in latitude, so far as these limits depend upon temperature alone, are those points at which a certain sum of positive temperatures can be attained between the first and the last killing frost. The northern and southern boundary lines of such a limiting area are the curves corresponding to two very different sums total of positive temperatures, the northern limit having a smaller sum and the southern limit a larger, beyond either of which the plant is unable to modify its internal organization so as to properly utilize the respective prevailing small or large quantity of heat.

Linsser notes that different plants, especially those that blossom early in the year, show a strong tendency in certain years to blossom a second time, and he finds that when the excess of the total heat in a favorable year exceeds the normal annual total by a quantity equal to that ordinarily required for the first blossom (and this can easily happen on account of the small sum required for the early spring blossom) then the plant produces a second blossom.a

In regard to the effect of daylight as such, Linsser says the opinion has been expressed that possibly the duration of the daylight, which, during the growing period, increases as we go northward, must compensate for the diminishing sum total of heat; but his figures show nothing of this influence, since the discrepancies or departures between his observed and computed figures have altogether the character of accidental errors. In fact, his law of the constant quotient or percentage of heat implies that the plant does not need any compensation as the heat is diminished, but directly adapts its cycle of operations to the diminished sum and transmits this power to all further generations. In addition to this, however, since the importance of light to the plant is proven, it is necessary to remember that with the increasing duration of the day as we go northward there is a steady diminution in the intensity of the daylight because

a Ought we not to infer from this that after a perennial plant has received sufficient heat to blossom and eventually to ripen its fruit it then at once begins to repeat this cycle of processes, and is ordinarily only delayed by the cold of winter? If this is true, it must be considered that with the warm weather of spring the plant takes up these vital processes at the point where they were left in the autumn. Therefore, in such cases, our sums total of temperature, moisture, etc., should all begin to be counted with the ripening of the fruit, or the fall of the leaf, and not merely with the opening of vegetation in the spring.-C. A.

the sun's altitude diminishes. This Linsser shows in the following table."

In reference to the first part of this table Linsser remarks that the intensity of the light of the sun varies as the sine of the angular altitude of the sun, so that from the maximum altitude on any day we get an approximate idea of the influence of sunshine; and we see also that the farther north we go the longer duration of the sunshine is partly counterbalanced by the diminishing intensity of its influence."

Linsser remarks that the theory of compensation between duration of the day and intensity of sunshine may also be tested by considering the effect of ascending a mountain, where there is no increase of duration but a great increase in the intensity, of sunshine. If the rapid development of the plants on the mountains is due to the increase in the intensity of the light, then how can the diminution of intensity in northern regions bring about the rapid development that is demonstrated in the experiments of Von Baer and Schuebeler and Ruprecht which are quoted and analyzed in the following paragraphs?

a To which I have added three columns of relative intensity of the total heat received in twenty-four hours on each date, as interpolated from Angot's tables, for a coefficient of transparency equal to 0.70.—C. A.

The exact figures that give the relative sum total of the direct sunshine and the diffuse daylight for various latitudes and solar altitudes for clear and cloudless days have been published by Marie Davy, Angot, Wiener, and others. The figures that I have given in the last part of the above tables from Angot show still more clearly to what extent the effect of sunshine diminishes as we approach the pole, but how surprisingly powerful are the consecutive twentyfour hours of sunshine on June 15 within the Arctic Circle.-C. A.

In his second memoir Linsser (1869) begins by showing that many well-recognized facts have been found which harmonize with the conclusions at which he had previously arrived. Thus, in the first and second halves of the eighteenth century the northern limit of the cultivation of grain had not passed beyond latitude 60° 30′ N., and many unsuccessful attempts had been made to ripen the grains in more northern regions; but in 1829 Erman found a small successful beginning going on at Yakutsk, and since then it has spread in all directions and has extended to barley, oats, rye, and wheat. Similarly in Lapland the cultivation of grain succeeded only for a long time in the southern regions, but now it extends to the north and even among the mountains. In Lapland this cultivation succeeded only when the seed was brought from near by, not from a distance, and Von Baer says that it was commonly said that the grain had acclimatized itself, or, as he expresses it, "It seems to me that gradually a quick-ripening variety or 'sport' has developed that is not injured by the early frosts of summer nights."

F. C. Schübeler (1862) in his memoir on the cultivated plants of Norway states that in 1852 the seed of yellow maize brought to Norway from Hohenheim, near Stuttgart, was sown on the 26th of May and reaped one hundred and twenty days later, but after continued annual cultivations, in which every harvest came a little earlier than its predecessor, Schübeler, in 1857, sowed the seed on May 25 and harvested it in ninety days, while the seed of the same variety brought fresh from Breslau and sowed on the same date ripened only after one hundred and twenty-two days. Even Kalm had remarked that maize when transported from a southern to a northern latitude gradually overcomes the difficulty of ripening and eventually gives a nearly constant variety of grain.

Morren, in the Belgique Horticole (1859-60), says the principal problem to be resolved in Norway in the amelioration of its agriculture is the introduction of new varieties and the development of precocity. This precocity increases year by year, as if the plant could not all of a sudden obey the new climatic influences under which it had been brought. Plants cultivated many years in succession under a northern climate when transported to a southern climate preserve something of their former rate of development and are more precocious than plants of the same species that have remained in their first situation. Just as wheat carried from Germany northward into the Baltic Provinces of Russia fails to ripen its grain, so grain carried from the valleys up to the highlands in Switzerland fails to ripen.

Bastian quotes an old English author who says that in the acclimatization of plants the graduation of the process is the principal necessity, and that a sudden acclimatization in a new home is impossible, so that a plant gradually learns to live in a climate in which