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Another study into the total radiation received by the plants in sunshine was made by Gasparin by placing a thermometer in the center of a globe 1 decimeter in diameter, made of thin copper and covered with a layer of lampblack. Having found by comparison that bulbs of different sizes gave different temperatures, he recommends this size to all meteorologists; but I do not know of observations made by others until Violle (1879) urged the same construction and size for his conjugate bulbs. This bulb in the full sunshine and at a standard distance above the ground seemed, to Gasparin, to give what he calls the temperature of a dry opaque body. The difference between this and the temperature of the air gave a surplus showing the effect of solar radiation on the leaves; again, the difference between this dry, black. bulb and the temperature of the surface of the moist earth gave him some idea of the nature and amount of the influence of the sunshine on the surface of the soil, which he illustrates by the following table, derived from seventeen years of observations:
6.7 12.7 19.1 25.5 27.6 40.9 45.3
15.4 22.0 28.5 29.4 34.4 39.4 43.4
44.1 38.9 28.7 19.4 15.4
On this table Gasparin remarks:
We see how much the difference of temperatures of the stems and the roots ought to modify the flow of the sap, and there is here an interesting subject for physiological study which should redound to the profit of agriculture. The solar heat contributes also in a remarkable manner to cause the differences in the vegtation of the mountains and the plains. On mountain tops it is the heat of the surface soil and the roots in the sunshine and the effect of sunshine on the leaves that makes possible the existence of a great variety of phænogams. The direct action of the solar heat is the explanation of the possibility of raising cereals and other southern crops in high northern latitudes.
Gasparin (1852, p. 100) gave the following table, compiled for western Europe, showing the mean temperatures of the day during which the respective plants leaf out, flower, or ripen. This early effort to apply meteorological data to the study of plants takes no account, as the author himself says, of other meteorological conditions than temperature such as introduce considerable variations into the phænological phenomena, but he gives it in hopes of helping thus to fix the rela
tions of natural vegetation to cultivated plants. If in addition to
climates (by Gasparin).
°C. Wild honeysuckle (Lonicera peryclimenum)
2.0 Thorny gooseberry (Ribes uva crispa)-
5. O Lilac
5.0) Ordinary currant (Ribes rubra)
6.0 Broad-leafed willow (Salix capræa)-
6.0) Horse-chestnut (Æsculus hippocastanum).
7.5 Apple tree (Malus communis ); cherry tree (Cerasus communis)
8. O Fig tree (Ficus carica).
8. O Grapevine shoots
9. Mulberry tree covered with leaf-buds; walnut tree_
9.8 Sprouting of lucerne grass.
10.0 Alder tree_
12. 0 Oak; mulberry tree developing leaves.
12. 7 Acacia (Robinia pseudoacacia)-
13. 3 (2) FLOWERING. Hazelnut tree (Corylus avellana) ; cypress
3.0 Furze or gorse (Uler europaeus); box (Buxus sempervirens); white poplar (Populus alba)
4. 0 Broad-leafed willow ; honeysuckle--
5. O Peach tree---
5.4 Almond tree; apricot tree.
6. 0 Pear tree -
7.0 Elm; apple tree.
7.5 Cherry tree; colza
8.0 Lilac; strawberry plant
9.5 Broom (Genista scoparia)
10. O Beans
11. 5 Isorse-chestnut.
12. 0 Hawthorn or may (Mespilus oxycantha).
12.5 Sainfoin or French grass (Hedysarum onobrychis, Leguminosä) -
12, 7 Acacia (Robinia)
14. 0 Rye
14. 2 Buckthorn (Rhamnus paliurus).
15. O Oats.
16. 0 Wheat; barley
16. 3 Chestnut tree:
17.5 Grapevine: Full flower
18. 2 Flower passed
19.0 n corn; hemp; olive tree_
(3) RIPENING. Iuring increasing heat: Fruit of the elm tree
12. 0 Green peas
14. 2 First cherries; broad beans_
16. 0 First mowing of sainfoin
17.0 Currants; raspberries; strawberries; cherries.
17.8 Morella cherry tree; apricot; plum tree; barley ; oats.
18. 0 Rye
19. O Peach tree; harvest of corn.
20.0 First figs ; green gage plums.
21. 0 First grapes, called madeleine; melons in free earth..
22. 5 Hemp
22.6 During decreasing heat (for fruits which have received a sufficient quantity of increasing heat)': Horse-chestnut
18. 2 Indian corn ; potatoes
17.0 Walnuts and chestnuts
16. 2 Pomegranates_
15. 0 Saffron
13. O Olives
10. O NOTE.—It can be easily understood that the fruits which require the greatest prolongation of heat ripen last and are gathered at periods of the lowest temperatures.
Lachmann, in his Entwickelung der Vegetation, counts the sum total of all the temperatures at his station (Braunschweig, Germany) from February 21 onward.
Linsser, for north temperate countries, counts from the date when the temperature 0° C. is attained, but for warmer countries he counts from the date when the lowest temperature of the year is attained; which date would, according to his calculations, be the 8th of February at Braunschweig instead of the 21st of February; but, according to the normal values resulting from the thirty years of observation by Lachmann, this change would only make his sum totals about 10° C. larger.
Tomaschek, as quoted by Fritsch (1866, LXIII, p. 297), takes the mean of all positive temperatures as observed at 6 a. m., 2 p. m., and 10 p. m., omitting the individual negative observations instead of the negative daily averages. He counts the sums from January 1; this method gives figures that agree very closely, at least in Europe, with those given by Fritsch's method.
Kabsch, as quoted by Fritsch, attempted an improvement on the method of Boussingault. His formula is especially appropriate to the annuals, but not to the perennial plants. His method of computing the thermal constant is expressed by Fritsch in the following formula:
where the notation is as follows: C is the total heat from the date of sowing up to the date of sprouting; a is the thermal constant from one phase to the next, such as from sprouting to flowering; t is the number of days from sprouting to flowering; c is the mean daily temperature from sprouting to flowering; t c is the total sum of mean daily temperatures from Sprouting to flowering; as this temperature is - - - -* . principally active during the daytime, therefore one-twelfth of t c represents the efficient heat during an hour; h is the duration in. hours of an average growing day, viz, from sunrise to sunset; therefore one-twelfth of the product c h t represents the total heat that has been utilized by the plant. The method of reasoning by which Kabsch arrives at the above formula, which I have quoted from Fritsch, is not known to me. Sachs, by direct experiment, finds that for each plant there is a temperature most favorable to its growth and two other limits, minimum and maximum, beyond which it will not grow. Deblanchis finds that the temperature on which vegetation depends is not the ordinary temperature of the air as given by a sheltered thermometer; he prefers to approximate to the temperature of the leaf of the plant by the use of his “ vegetation-thermoscope,” which is an ordinary minimum thermometer covered with green muslin and kept moist, as in the ordinary wet-bulb thermometer. He places his thermometer at one and a half meters above the soil and in full exposure to sun and sky. Evidently the sum total of his temperatures will be between the sums of the ordinary wet-bulb and the ordinary dry-bulb thermometers, but must differ greatly from the temperature of the roots on which the growth of the plant primarily depends. Hoffmann prefers to take for the daily temperature the excess above freezing of the maximum thermometer exposed to full sunshine and free air. Hoffmann's temperatures approach more nearly the temperature of the roots within a few inches of the surface of the ground. Besides taking the sums of the average daily temperatures of the shaded air thermometer, omitting all negative values or all those below freezing point, Hoffmann also took the sum of the bright bulb in vacuo and of the black bulb in vacuo, both in full sunshine; these latter temperatures are generally higher than those of the roots and much higher than those of the leaves. Hoffmann prefers to use the readings of the bright bulb in vacuo. Hervé Mangon (1879) modifies Gasparin's method slightly in that he takes account of the shade temperatures of the air from the date of sowing up to the date of harvest, rejecting all cases where the mean daily temperature in the shade is less than 6° C.; he had been led to think that the vegetation of cereals and other important crops ceases below this temperature. Thus he determines the sum total
needed for ripening the crops of the varieties of wheat ordinarily cultivated in Normandy, as shown in the following table:
By similar calculations Hervé Mangon obtains for other crops as cultivated in Normandy the following results:
atures Harvest from Sowing.
sowing to harvest.
Mar. 7 Aug. 5
1,826 2,197 1,810 2,210 1,525
Hervé Mangon concludes his essay with two important practical rules, deduced from his data relative to the climate and crops of the department of La Manche: (1) In a mild and uniform climate, like that of the northwest of France, there is always an advantage in sowing the seed early in the autumn; (2) by computing annually the sums of the degrees of temperature observed since the date of sowing and by consulting the numerical tables given in this memoir one can, with great accuracy, calculate four or six weeks in advance the date of the approaching harvests of the respective plants.
The tables given by Mangon for his locality can be reproduced for American stations wherever the meteorological observations and the dates of planting and harvesting are recorded; although it may be possible to consider more minute details of climate and soil than he has done, yet the success attained by him in his elementary collation of fundamental data must stimulate to similar work in this country.