Transactions of the Londoii Horticultural Society. 507 



It is well known, that plants in a state of growth suffer more from frost, 

 than those which are dormant. I have seen young shoots of the oak, and 

 ash, blackened by frost in the month of June, in the hedgerows of Norfolk 

 and SuiFolk, and yet we know how capable are those natives of the soil of 

 resisting with impunity our severest winters. This is undoubtedly owing in 

 a great measure, if not exclusively, to their tissue containing much more fluid 

 when in a growing state, than when they are dormant. The more succulent 

 a plant, or a part of a plant, the more tender it is under equal circumstances. 

 An oak, or an ash, is nearly exhausted of its fluid contents by the leaves, 

 before the frost sets in, and, in fact, the fall of those organs in deciduous trees 

 is probably caused, in part, by the inability of the stem to supply them in 

 autumn with an adequate quantity of fluid food ; during the winter, but little 

 water is added to the contents of the stem, ifhtil after the severest frosts are 

 past and the return of spring, when the sap is attracted upwards by the bud- 

 ding leaves. The winter, therefore, is the dry season of such plants, and for 

 that reason the period in whicli they are least liable to the effects of frost. 

 But if any unusual circumstance alters this habit, the capability of resisting 

 frost is altered with it ; and thus the arbutus, the vine, the araucaria, and 

 the other plants mentioned in the instances lately quoted, stationed in warm 

 , sheltered situations, were stimulated prematurely into growth, their stems 

 were filled with fluid, and they were, in consequence, affected by frost in a 

 much greater degree than when, from the coldness of a station, they were 

 kept in their ordinary winter condition. 



Nothing seems more generally to have excited surprise, than that so many 

 plants, apparently killed, sprang up again from the roots. Hence it has been 

 generally said, that many species which would have survived, if undisturbed, 

 were thrown away, in the eager haste of gardeners to remove objects, which 

 had become unsightly. Some have indeed ignorantly imagined, that the mere 

 act of cutting dead stems down had the effect of destroying the lingering 

 vitality of the root. No person, in the slightest degree acquainted with the 

 nature of vegetable life, could entertain such an idea as the last ; but for the 

 first, there is no doubt some foundation. In all cases, the roots of trees 

 suffer from frost less than the stems, partly perhaps because the vitality of a 

 root is greater than that of a stem, as Mr. Knight long since showed ; but 

 more especially because they are so much less exposed to cold. That the 

 earth, being a bad conductor of heat, should remain in winter at a higher 

 temperature than the superincumbent atmosphere will excite no surprise ; 

 but probably few persons are aware to how small a degree the temperature of 

 the earth is lowered in this country, during even long-continued and severe 

 frost. In order to measure the exact difference between the temperature of 

 the earth, and the air, experiments have for some time been in progress in 

 the Society's Garden. Two thermometers have been buried in the earth, 

 one at the depth of 1 foot, the other at the depth of 2 feet, and their 

 indications have been noted daily. It will be seen, from the following table, 

 that the ground was never frozen to the depth of a foot, in the Society's 

 Garden, even while the temperature of the surface was as low as 4|° below 

 zero, and that it did not fall to within 5° of freezing at the depth of 2 feet 

 during the same period. I cannot pretend to explain the discrepancy between 

 this statement, and the observations of those who have found the earth frozen 

 to the depth of more than 2 feet during the past winter, especially, as the 

 soil in which my observations were made is far from dry ; but the fact as now 

 stated is certain. In order to check the geothermometrical observations, I 

 caused the earth of the garden to be broken up during the frost, for the 

 purpose of ascertaining how deep the soil was hardened, and the result was 

 as follows : — 'In the Kitchen-garden quartei", 9 inches; in a hard loam foot- 

 path, 10 inches ; in the Arboretum, adjoining the geothermometers, 8 inches ; 

 in the Arboretum, where the turf is chiefly composed of moss, 5 inches. 



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