THE FARMER'S MAGAZINE, 



381 



plants really are, we find that, like animal, they 

 must have their constant periods of repose. Win- 

 ter to them is an annual night, as to ourselves is 

 a period of daily rest. We cannot with impunity 

 break in upon these natural habits. When we 

 attempt it, we see vines yielding watery wood and 

 colourless fruit; cucumbers emaciated and barren. 

 "We have shown," remarks a practical gardener, 

 Mr. W. P. Ayres, in his work on the cucumber, 

 "that the cucumber will sustain no injury at a 

 temperature of 55 degs. during the night, and we 

 are certain the plants will be more vigorous and 

 continue longer in a bearing state in a low than if 

 a high night-temperature was maintained." 



Similar observations to these were long since 

 made by T. A. Knight, the celebrated President of 

 the Horticultural Society. These indeed were the 

 kind of researches in which Knight showed him- 

 self so much in advance of the commonly enter- 

 tained notions of his daJ^ 



He told the fellows of the Horticultural 

 Society, when addressing them "on the ill effects 

 of excessive heat in forcing-houses during the 

 night," — " Being fully sensible of the comforts of a 

 warm bed on a cold night, and of fresh air on a 

 hot day, the gardener generally treats his plants as 

 he would wish to be treated himself : and conse- 

 quently, though the aggregate temperature of his 

 house be nearly what it ought to be, its temperature 

 during the night, relatively to that of the day, is 

 always too high. The consequences of this excess 

 of heat during the night are, I have reason to be- 

 lieve, in all cases highly injurious to the fruit trees 

 of temperate climates, and not at all beneficial to 

 those of tropical climates, for the temperature of 

 these is, in many instances, low during the night. 

 In Jamaica, and other mountainous islands of the 

 West Indies, the air upon the mountains becomes, 

 soon after sunset, chilled and condensed, and, in 

 consequence of its superior gravity, descends, and 

 displaces the warm air of the valleys. Yet the sugar- 

 canes are so far from being injured by this sudden 

 decrease of temperature, that the sugars of Jamaica 

 take a higher price in the market than those of the 

 less elevated islands, of which the temperature 

 of the day and night is subject to much less varia- 

 tion." 



The effect of temperature on vegetation has also 

 engaged the attention of several continental philo- 

 sophers. Humboldt has many interesting notices 

 of this kind dispersed through his valuable works. 

 De Candolle had watched the influence of tempera- 

 ture in promoting or retarding the growth of indi- 

 genous plants. He had traced their presence from 

 the sea-shore to considerable elevations, from high 

 to lower mean temperatures. He too, in common 

 with the English farmers, was well aware of the 



effect of elevation in compensating for latitude in 

 the growth of vegetables. He remarked that when 

 plants, not suited by their nature to support an ex- 

 cess of either heat or cold, are found to grow in dif- 

 ferent latitudes, it is always at such heights as that 

 the effect of elevation compensates that of the 

 latitude. The Saxifrucja r/reenlandica he found 

 growing on the summit of the Pyrenees, at an ele- 

 vation of from 2,500 to 3,278 yards above the sea. 

 The Spanish chestnut, which only grows on the low 

 lands of the north, flourishes on the hills of the 

 south of France, and at still greater elevations on 

 the Appennines and on Mount Etna. 



Cultivated plants are under a like influence as to 

 elevation. They car. only be successfully grown 

 at such heights as correspond in temperature to 

 that of the district to which they belong. As a 

 general rule, it may be, perhaps, considered that a 

 degree of latitude affects the mean temperature 

 nearly in the same proportion as 180 or 200 yards 

 in the elevation. This rule is, however, modified 

 by various local circumstances. De Candolle 

 tested, by this rule, the growth of some of the cul- 

 tivated crops of the French farmers. He found 

 that the highest spot at which maize (or Indian 

 corn) is grown in France, is at the village Lescan, 

 in the department of the Pyrenees, at an elevation 

 of about 1,000 yards above the sea. Now, if we 

 take our departure from that point, which is the 

 forty-third degree of latitude, and proceed five de- 

 grees upon the same meridian line, we come to the 

 neighbourhood of Mans, and to the south of the 

 departments of lile and Vilaine, which are precisely 

 the northernmost points where maize is used for a 

 crop. 



The vines of Vela are perhaps the highest vine- 

 yards in France ; the elevation of the town of Pay 

 is computed at 632 yards, and the vineyards that 

 belong to it go up to about 800. Now, if setting 

 out from that point, which is a little beyond forty- 

 five degrees of latitude, you take four degrees to 

 the north upon the same meridian, you come to be- 

 tween Rheims and Epernay ; that is to say, very 

 close upon the northernmost limit at which the 

 vine forms a branch of husbandry. With regard 

 to the olive tree, the local peculiarities of the coun- 

 tries where it grows are such as to make investiga- 

 tions of this kind very intricate: it is generally 

 cultivated in parts protected on the noTth by some 

 vast range of mountains, where the mean tempera- 

 ture is consequently higher than it would other- 

 wise be. When it is not sheltered by any range of 

 mountains, the" northernmost point in Europe at 

 which we find the ohve is Ancona, in 43«' 37' of 

 latitude. In respect to the other points of view, its 

 positions have been measured in several parts of 

 Roussillon, Languedoc, Provence, and Italy ; and 



