324 THE FLORIST. 



with the surface of this substance, otherwise they will derive little 

 advantage from it. Now the earth is an absorber of this kind, but it is 

 practically inconvenient to have the trees so trained as to be in contact 

 with it ; besides which, the rapidity with which it loses heat by radia- 

 tion during the night, and its exposure to the most severe effects of 

 hailstorms, &c,, render it inapplicable. The brick wall next suggests 

 itself; and we may believe in the wisdom of our forefathers, who dis- 

 covered all its good qualities — namely, its quiet absorption of heat, 

 which it gradually gives out again, when the sun ceases to shine upon 

 it, and the surrounding atmosphere is cooler than itself Then, again, 

 its perpendicular position guards it in a great degree against loss from 

 radiation, and this saving of heat is much assisted in well -finished walls 

 by means of a projecting coping of some kind. 



We have gone somewhat out of our way in laying down the rationale 

 of the wall, as we had before assumed that it was a necessary protection ; 

 it will, however, be seen that this was requisite to form a groundwork 

 upon which to base further remarks. 



We had, moreover, assumed that it was insufficient generally, and 

 we may as well, beforeT going further, consider why it is so. The loss 

 of heat is still so great during the clear nights of early spring, before the 

 leaves of the trees have covered the walls enough to form of themselves 

 a non-conducting covering, that the young shoots and blossoms are 

 Hable to be injured in various ways ; especially as the difference is 

 greater than under natural circumstances it would be, owing to the 

 stimulating effects of the heat- accumulating wall during the day, and 

 especially at those times when the earth in general returns so much of 

 its heat to the bright clear sky, that the peculiar state of things w^e call 

 " sharp frost " becomes an existent fact. 



Well, we are still only bringing up the rear ; our grandfathers found 

 all this out, and, as protectives, adopted the various modes of straw 

 curtains. Fir branches, canvas blinds, and many others, and generally 

 succeeded in securing a respectable crop. It ' is, however, generally 

 admitted that our springs are more precarious from their changeableness, 

 if not upon the average colder, than they were m older times. It is, 

 besides, generally expected that with our advanced knowledge and our 

 improvements in arts and sciences, we should do more in the way of 

 artificial cultivation than merely " secure respectable crops sometimes,''^ 

 for with our ordinary apphances the ''generally " alluded to above has 

 thus degenerated. The obvious common argument is, that in the present 

 day we ought to be more than a match for the difference apparent in 

 in our seasons, that what is done sometimes may be done always, ought 

 to be reduced to a certainty. 



To proceed thus, having mentioned the advantages of the simple wall, 

 and considering that without it we should lose them all, we may conclude 

 that it is indispensable as a foundation for our scheme, and that all that 

 is necessary further is to enclose it with a glass case, the latter containing 

 between itself and the wall a body of air which, if the case is closed, will 

 remain quiet and prevent the rapid loss of heat in windy weather, un- 

 avoidable under any mode of covering which the air can freely penetrate. 

 The enclosure of a body of air in contact with the wall moderates very 



