226 
Cold frames, which are pits for the preservation of tender 
plants, without fire, are constructed upon this principle. A 
friend of ours has succeeded in preserving a very considerable 
collection of camellias in the open air in a thin hoard frame 
without artificial heat, and with only the slight covering of the 
common frame lights and a few layers of mats above them. 
During winter this was scarcely ever opened, except occasion- 
ally, to admit the air, but never the sun, and, at the approach 
of spring, the frame was again subjected to the full influence of 
the sun and air in the most careful and gradual manner. 
Such half hardy trees or shrubs as the Acacia julibrissin, 
the white European jasmine, &c. may be kept in fine condi- 
tion, simply by sheathing them with straw at the approach of 
winter. Even the Lagerstraemia indica, and Aucuba japonica, 
may be kept in full vigour in the open air, in this latitude, by 
this practice. Some of the more tender magnolias require and 
amply repay this trifling care, and almost every half hardy 
shrub, or tree, may be carried through the most inclement 
portion of our year, in a state of comparative security in this 
manner. 
It is well known to those who have made many experiments in 
the naturalization of half hardy trees or shrubs, that the suc- 
cess with which they withstand the effect of intense cold de- 
pends mainly upon the complete maturity of the young wood. 
Should the shoots of the current year, even of our more hardy 
trees, be caught by an untimely frost, before they have ripened, 
they will suffer greatly by the combined action of the frost and 
sun upon the well filled and immature sap vessels; while, on 
the contrary, even comparatively tender trees will withstand 
very severe cold, if they are furnished only with sound mature 
wood. This will point out to the culturist the necessity of 
placing the half hardy shrub or tree upon a dry and warm sub- 
soil, where it will not be likely to be urged into late growth 
by excessive moisture of the soil. In such situations, natural- 
ization of tender trees may be carried on with the best hopes 
of success. 
Nearly all half hardy trees will require the sheathing of stra\v 
before mentioned, over the whole of their exposed stems and 
branches while they are yet young; as the tree advances in size, 
only the upper branches will probably need protection until. 
