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ought to be made in this case for the less favorable meterological conditions during the time this plant was used, as shown by the table.

Again, it is very probable that in plants with evergreen leaves having thick epidermal tissue evaporation is only possible through the stomata, whereas in the case of leaves which are thin, soft and rapidly growing, with little cortical tissue, evaporation is more general from their surfaces. It is quite possible, also, that the number of stomata in the case of the Camellia is below the average. However these things may be, the fact remains, that the nature of the cuticular tissue of the leaves is hereby shown to be closely related to the amount of liquid transpired.

This plant exposed during a cloudy and dewy night gained in weight to the extent of 310 gr., as shown by the table; the same thing occurred on a rainy night in the house, when the plant was situated about four feet from an open window, as was the case in all indoor experiments; the gain in the latter case, as shown by the table, being 230 gr. There was no loss by evaporation at night

in the open air.

Plant No. 6, was a Lantana (L. carnosa), a shrubby plant, 18 inches high; leaf surface 330 square inches; weight only 11⁄2 ounces; complete weight fitted for experimentation, 5 pounds 2 ounces 250 grains.

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The leaves of this little plant were very thin and soft, which may account, in a measure at least, for the great rapidity of transpiration from their surfaces. As compared to the extent of leaf surface, this plant evaporated more than any other plants tried, reaching, in a clear windy day, nearly 2 ounces per square foot of leaf surface in twelve hours. It will be observed that the Lantana evaporated nearly three times its own weight in twelve hours.

A few experiments were made with this plant (as was done with the Hydrangea) to ascertain how much more rapid the process was about midday than at other periods of the day. It was found

to be most rapid about noon and a little after; and it was found here, also, that half the quantity evaporated by day was given off between the hours of II A. M. and 3 P. M. These observations were made on clear days.

The last, or plant No. 7, was a Dracana, an herbaceous plant with large leaves (being cultivated for its foliage). Its leaf surface was estimated at 817 square inches; its height 27 inches; weight not taken; complete weight of outfit, II pounds 6 ounces. The following are the results obtained:

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In comparison to the extent of leaf surface, this plant did not transpire as fast as most of the other plants used. The fact of the Dracæna having smooth and more or less hard leaves, no doubt. accounts for the relatively less rapid evaporation from its surface. In the case of the two last plants tried, it may have been noticed, as in the two before them, that, other things being equal, dryness of the atmosphere was favorable to the process of transpiration.

In experiments IV and V, with both the Lantana and Dracaæna, are shown once more the favorable influence of winds over this process in plants. The scales used in all these experiments were accurately adjusted.

Summary of Investigations.

In clear weather the evaporation by night as compared to that which takes place in the day appears to be about in the ratio of I to 5. In some cases no loss occurred on dewy or cloudy nights. The Camellia, however, lost nothing during clear nights, and gained in weight on dewy or rainy nights, even when kept indoors. Under ordinary circumstances evaporation at night was about the same indoors as in the open air.

The rate of transpiration during the day showed a very different relation, giving a ratio of 2 to 1 in favor of the open air. Of the whole amount evaporated during twelve hours, in the day experiments, half was given off between the hours of 11 A. M. and 3 P. M., as shown by repeated testing.

The following table, compiled for the number of clear days, will serve to exhibit the average rate of transpiration by day which took place in the open air during clear weather. It will also indicate the relation between leaf surface and the weight of the plant, and amount transpired.

The mean temperature and average dew point have also been recorded in the table.

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After an inspection of this table, the average rate of evaporation for soft, thin-leaved plants, in clear weather, may be put down at about 1/4 ounces per day (12 hours) for every square foot of leaf surface. The Lantana shows nearly 2 ounces to the square foot of surface. The Camellia, with its dense, smooth leaves, averaged less than half an ounce to the square foot of surface, per day.

The nature of the leaf structure modifies very greatly the rate of evaporation, as may be seen by comparing the results from the Camellia with those of other plants having soft and thin leaves.

Apart from structural peculiarities, no doubt the sun's rays stand first in importance among the modifying influences; for going back to the results from the Fuchsia, for instance, we find the average temperature higher and the dew point greater during the indoor experiments than when the plant was exposed, and yet the relation of evaporation in the two situations was, other things being equal, about as ordinarily the case. The same obtained in the case of the Hydrangea in a still more marked degree.

It is still an unsettled question whether radiation, as such, produces this great effect, or whether it is through the heat that accompanies the rays, or the chemical changes they produce.

That the difference between indoor and out of door evaporation was not due so much to atmospheric currents as to the action of the sun's rays, is shown by the fact that, during the ex

periments outside on a cloudy day, strong atmospheric currents did not by any means raise the daily quantity to what it was on a calm but clear day. But it must be remembered that currents are much more effectual in hastening the process in clear than in cloudy weather, for the simple reason that the sun's rays opening the pores of the plant, allow of the more ready escape of aqueous

vapor.

Of the influence of currents, then, it might be stated, from what has been observed, that in clear weather they are very effectual in favoring the process; in cloudy weather their influence is not so noticeable. On clear days strong currents increased the amount over that of calm days by about one-fifth or even onefourth.

It was found, in every instance tried, that, other things being considered, the complement of the dew point, or the dryness of the air, modified in a marked degree the rate of transpiration; and this appeared to be, in a measure at least, independent of the temperature, as the latter condition did not seem to affect perceptibly the amount evaporated, unless, as is usually the case, the relative humidity was correspondingly low.

A few calculations may serve to impress the importance of the ratio of transpiration, deduced from these experiments. According to the above rate the Washington Elm, at Cambridge, a tree, it is stated, of no very large size, with its 200,000 square feet of leaf surface, would transpire 734 tons of watery vapor in twelve hours (day) of clear weather.

Carrying the calculation further, a grove consisting of five hundred trees, each with a leaf surface equal to that of the elm. mentioned, would return to the atmosphere 3906 tons of aqueous vapor in twelve hours. Even supposing this to be much overestimated, it may very fairly be concluded from the facts given that the evaporation of watery vapor from plants is a powerful agent in maintaining the humidity of the surrounding air. And if the above data be correct, a strong argument is furnished in support of the belief that vegetation influences, in a great degree, the rainfall of a region of country.

The practical advantage of keeping plants in occupied rooms, in which the air is generally dryer than outside, has, also, from the results obtained, received further demonstration.

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RAMBLES OF A BOTANIST IN NEW MEXICO.

BY EDWARD LEE GREENE.

I.

SANTA Rita del Cobre is situated in the extreme south-western

part of New Mexico, amid the Santa Rita mountains, so rich in copper ore. It was in former times a Mexican penal colony where convicts did service in the mines; now, however, since the acquisition of that region by the United States, Santa Rita del Cobre has become a mere pile of adobe ruins; the crumbling walls, a group or two of neglected and very ancient looking peach trees, and the abandoned mines showing to him who passes through, that the place was not always the silent wilderness it now appears. New towns are at present springing up within a few miles, in different directions; for the American people have discovered rich silver mines not far from where the Mexicans found only the grosser and less valuable metal. It is an interesting region, the natural history of which has not been looked into except by the few scientists who have accompanied one or two government surveying expeditions in passing through it. Aglow with the ardor of a botanist in a new field of study, I entered this remote corner of New Mexico from the westward early in April. The broad expanse of plains through which runs the boundary line between this territory and Arizona was already decked with a profusion of flowers. The number of species was not great, but each species was represented by myriads of individuals, so that the whole prairie landscape seemed painted in lively colors. The plant most common of all was the smaller species of California poppy (Eschscholtzia douglasü Hook. & Arn.), one of the characteristic plants of the Pacific coast, hardly to have been looked for unless as a rarity so far eastward as this. In northern parts of California the Eschscholtzias sometimes grow in such abundance on the plains that sensitive eyes are dazzled and pained by the intense brightness of the mass of golden yellow bloom; yet never in California have I seen a landscape more brilliant with these flowers than were these level tracts away upon the borders of New Mexico. An albino variety, more pleasing than the normal yellow was frequently noticed, its petals not pure white but pale cream color, with a yellow spot at the base.

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