BOOK I. CULTURE OF THE CUCUMBER. 577 



The risk of burning the plants at first, as well as on the application of every fresh lining. In a few 

 days after a cucumber-bed has been planted, the "heat of the dung begins to decline, and perhaps the 

 weather changes from fine, and becomes cold, wet, and gloomy ; and in that case a lining of fresh dung 

 to enliven the heat of the bed is undoubtedly required. When this fresh lining is applied, it sets the bed 

 into a fresh fermentation, and very frequently gives too much bottom heat, and it even often happens that 

 the heat becomes too great under the plants before a lining is applied ; for the heat of a dung-bed is change- 

 able, and is raised and lowered by the changes of the weather. There is no necessity for having heat di- 

 rectly underneath the roots of the plants ; for if the air in the frames be kept up to a proper degree of heat, 

 that is sufficient. In climates where the cucumber naturally grows, I apprehend there is no heat in the 

 earth but what is raised in it by the heat of the sun and the circumambient air, which seems to be warmed 

 by the reflection of the sun upon the earth." 



The risk of destroying the plants by impure air, and steam from the bed. " It is not only necessary 

 that in the frames the air be kept up to a sufficient degree of heat, but it is absolutely necessary that nothing 

 pernicious or unwholesome be conveyed into, or caused to arise in, the frames among the plants by means 

 of that heat. If the steam of the linings get in, it will hurt the plants : and if there be any thing which 

 smells disagreeably in the mould, or underneath the mould in the frames, the heat of the linings will cause 

 unhealthy vapors to ascend from it, which in time will prove injurious to the plants. So that, although 

 there may be a degree of heat in the frames strong enough for the growth of the plants, yet, through means 

 of that heat, something may arise in the frames which will become progressively, if not almost instanta- 

 neously, destructive of the plants, especially when they are young and tender. Care, therefore, must be 

 taken that nothing be introduced into, the frames among the plants but what is of a sweet wholesome nature." 



The difficulty of keeping up the proper heat in winter. 



The great attention and expense attending the formation and general management of dung-beds in 

 winter. 



3239. The chief advantages of M'Phail's frame are stated to be : 



That the coldest place in the bed is exactly in the centre of each pit, from which centre the heat in- 

 creases on each side to the linings where the heat begins. The plants being planted, he says, in thii 

 centre, or coldest part of the bed, their roots can never be hurt by the heat increasing on each side gra- 

 dually, being in every respect suitable for their increase and extension. The heat in the centre of each 

 pit, just where the plants are first planted, seldom rises higher than to about eighty or eighty-five degrees, 

 nor does it ever rise higher in any part of the pits than about ninety-six or ninety-seven degrees ; nor do I 

 believe it ever can be raised higher than that, without scorching the plants by top heat or heated air : 

 whereas, in a bed made of dung, the heat in the centre of the bed, under the mould in which the plants are 

 planted, frequently rises to above 120 degrees, when, at the same time, the air in the frames can scarcely be 

 kept up to a proper degree of heat: this frequently happens in cold weather in winter. The scorching 

 heat ot a hot-bed of horse-dung, when too hot for plants, is equal to 130 degrees and more, and hereabout is 

 probably the heat of blood in fevers. 



The dung requires no more working than what is necessary to bring it to and keep it in a proper degree of 

 heat, and to let some of its more rancid qualities pass off by evaporation ; and as soon as the heat rises in 

 the linings, it circulates in the flues, and warms every part of the bed ; whereas the dung for making a 

 common cucumber-bed must be turned and worked, and lie, till, by fermentation, its rank qualities 

 be evaporated, and its violent heat be somewhat diminished. This, as already noticed, is a very great 

 advantage. 



The linings retain the heat longer than the linings of a dung-bed do, and that because the flues are con- 

 stantly full of steam ; but a dung-bed having little or no vacuity for the retention of the steam, the steam 

 of the linings of it is perhaps more immediately evaporated, and consequently the heat of the linings is 

 sooner exhausted than the heat of the linings of the brick-bed. 



In the course of the winter a dung-bed sinks so low, that it becomes difficult sometimes to get a 

 proper heat raised in the linings ; but my brick-bed being always of the same height, such difficulty can 

 never happen. 



A brick-bed may be built and set to work immediately ; the heat of the linings will dry the lime of 

 the joints of the bricks. The evaporation in the frames, from the moist lime of the joints of the brick- 

 work, has no bad effect on the plants ; but when a bed is set to work before it be dry and steady, great 

 care must be taken not to injure the brick-work in filling up the pits. 



All the materials of the brick-bed are clean and sweet; and the flues being m.ade perfectly close, no 

 tainted or bad-smelling air can get through them into the bed, so that it is of little or no concern whether 

 the dung of the linings be sweet or otherwise, or whether the linings be made of dung, or of any thing 

 else, provided there be a sufficient heat kept in them, and no pernicious steam be drawn in among the 

 plants by the current of air. 



3240. The plan of M' PhaU's frame has already been given and described. (1551. and 

 fig. 233.) It is almost needless to repeat that a sheltered dry situation for placing it is 

 of the first consequence. The bed being built, " when the frame is about to be set upon 

 it, a layer of mortar is spread all round upon the upper course of brick-work on which the 

 bottoms of the frames are to rest. Thus the frames are set in mortar on the bricks; 

 and the flues are, with a bricklayer's brush, well washed, and rubbed with a thick grout 

 made of lime and water, which stops every crack or hole, and prevents the steam of the 

 linings from getting into the frames. This washing of the flues I had done once a-year, 

 for no crack or hole must ever be suffered to remain unstopped in the flues. I found little 

 or no trouble in keeping the flues perfectly close, nor is it indeed likely that they should 

 become troublesome if the bed stands on a sound foundation, for the heat of the dung has 

 not that powerful effect on the flues, as fire-heat has on the flues of a hot-house ; because 

 the heat of dung is more steady, and not so violent as the heat of fire ; and besides, the 

 flues of the cucumber-bed are almost always in a moist state, which is a preventive in 

 them against cracking or rending. When the bed is first built, the pits are about three 

 feet in depth below the surface of the flues. These pits I had filled up about a foot high, 

 some of them with rough chalk, some of them with small stones, and some of them with 

 brick-bats : this is to let the wet drain off freely from the mould of the beds. After this 

 filling up with chalk, stones, and broken bricks, there is a vacancy in the pits about two 

 feet deep below the surface^ of the flues ; this vacancy I had filled to a level with the 

 surface of the flues with vegetable or leaf mould; and in putting it in, it was gently 

 pressed, to prevent it from sinking too much afterwards." 



3241. On the surface of the mould with which the pits were filled, " under the middle of each light, and 



Pp 



