10S Warmth and Moisture in Plant Structures. 



and mark the result; they, from additional moisture, will have 

 become so contracted, that any sash not pulled quite home at 

 the time of shutting up will be found drawn up possibly an 

 inch, and the lines of those drawn close in the first instance 

 will be so tightened that it is difficult to untie them, tightened 

 in fact, almost to snapping. Yet, recollect that these infallible 

 hygrometers, previously to being fastened, were steeped, if I 

 may so express it, in air containing moisture in its natural pro- 

 portions ; and it appears incredible to me that they should gain 

 this after-excess in an atmosphere destitute of it, nor can I well 

 conceive how living vegetables can be starved for want of that 

 which inert vegetable matters, confined in the same place, re- 

 ceive in such superabundance. 



Then, in conclusion, I contend that, were the evil not over- 

 rated, the application of perfect preventives would be pro- 

 ductive of beneficial results; but this is not the case. I do not 

 speak this unadvisedly, it is a conclusion that has been forced 

 upon me by experience, in defiance of previous prepossessions 

 to the contrary ; after a constant trial of five years' duration, and 

 after paying all the attention I am capable of to the subject 

 during that time, I do not consider them beneficial. My pre- 

 decessor considered them highly injurious ; I do not go so far 

 as this, but admit that, without great caution in using them, 

 they would no doubt prove so. The preventives of radiation 

 mentioned consist of well, made wooden shutters, fitted as 

 closely as most parlour doors, perfectly water-tight, and all but 

 air-tight, and being, when applied, about 2 in. from the glass. 

 The space between soon becomes filled with heated air, render- 

 ing them most economical, and capable of affording a most 

 comfortable security during seasons of extreme severity; and in 

 these respects they have my warmest approbation. But I have 

 only been considering them as auxiliaries to the creation of 

 congenial atmospheres for plants, and finding that they very 

 materially lessen the supposed cause of an ungenial one, without 

 producing a corresponding improvement, I have concluded that 

 the cause is undeserving of the importance that has been 

 attached to it. Without extreme caution in the application of 

 such preventives, the worst effects will soon become apparent. 

 Although I am not prepared to say why, I find that, upon the 

 shutters being put on, the internal temperature is raised about 

 five degrees or thereabouts in ordinary circumstances, in cases 

 of cold rain or high winds more, therefore the injury they cause 

 may probably proceed from this ; the plants are enclosed in total 

 darkness, with an almost instantaneous and most unnatural in- 

 crease of temperature, in some measure maintained through the 

 night, and the same amount of depression when the shutters are 



