REFERENCE TO HORTICULTURE. 



75 



trees^ according to the nature of the plant. For those that spring early, and 

 are apt to be nipped by spring frosts, a north border and cold soil are best to 

 retard their time of starting till the danger from frost is less : for those that 

 suffer from want of the wood being ripened sufficiently, as many American 

 plants which have a warmer summer in their native situation to ripen the 

 M^ood, as also for those that suffer by autumn frosts before the wood is 

 ripened, a south exposure and warm dry early soil are best : in dry soils 

 there is not so much wood made, but that which is made is more easily 

 ripened ; and the more sun, the more likelihood that the wood will be 

 ripened before frost sets in. In some late wet autumns, some of the hardiest 

 of our trees have been killed : transplanted Birch, after being some years 

 transplanted ; Oaks, that were apparently sound, dying down half their 

 length in the ensuing spring ; and seedling American Oaks dying off in the 

 ensuing summer, after having begun to grow ; thus showing that even the 

 hardiest of our trees may be affected, from their wood not being sufficiently 

 ripened in a cold wet autumn. 



289. The presence of a stream or river is generally allowed to increase 

 the tendency to slight frosts in spring and autumn. The surface of the 

 water ^ as it condenses by cold, descends to the bottom, and a warm stratum 

 succeeds to the surface ; and so far the tendency is towards heating rather 

 than cooling the air : but the great evaporation that takes place througli the 

 day, and early in the evening, robs the air of so much caloric, that fields 

 situated near shallow rivers, streams, or bogs, have generally been found 

 most liable to frost ; near the sea, or near great bodies of deep water, the 

 first -mentioned effect of a succession of warmer strata to the surface pre- 

 vails, and we have less tendency to freezing. 



240. Watering in the morning early, if the frost has not penetrated to the 

 juices of the plant, may, by washing off the cold dew, prevent the frost 

 from penetrating ; and covering from the sun may save a plant partially hurt 

 from the excessive change of temperature, if a bright sunny day succeed the 

 frosty night : but no power on earth can recover the plant if the juices have 

 been exposed by freezing till the vessels are burst, which may be known by 

 the change of colour in the leaves by the suffusion of the sap. If some of 

 the most tender leaves only are hurt on the young growths, the plant may 

 survive ; if the wood is generally young and succulent, as in seedlings, 

 Dahlias, &c., the whole plant generally perishes, unless where there is an 

 old ripened root or wood to renew vegetation. Some plants, as Beech, that 

 throw out or evolve most of their young buds in spring, are apt to perish, 

 even though some years old, before the latest buds can spring : the Oak, 

 Ash, c%c., that have always spare buds, are not so apt to perish." (Gard. 

 Mag. vol. xvi. p. 430.) 



241. The general conclusions to be drawn from the observations contained 

 in this section are : 1, that the heat of the soil and of the free atmosphere 

 may be increased by diminishing evaporation, so as to receive a greater ad- 

 vantage from the rays of the sun ; and 2, that it may be preserved by 

 checking radiation. The means for diminishing evaporation arc draining, 

 improving tlie constituent parts of the soil, and shelter from cold winds ; and 

 the means of diminishing radiation are simply coverings placed over the soil, 

 or the plant about which the heat is to be retained. 



