Heating 



( 401 ) 



Hedera 



supply may be automatically regulated, and a 

 constant and regular heat thus ensured for any 

 reasonable length of time without attention. It 

 must be remembered, however, that the fumes 

 given off by oil and gas in combustion are highly 

 injurious to plant life. Elaborate precautions have 

 to be taken, therefore, to bottle up, condense and 

 burn, or get rid of these products of combustion. 

 In some of these heaters the fumes are made to 

 pass through a series of purifiers, and as long as 

 these are in working order the plants in the house 

 will take no harm. An exceedingly handy prop- 

 agator in which cuttings of many tender plants 

 may lie speedily rooted may be heated by means of 

 a small zinc tank of water standing over a lamp. 

 If this propagator is placed inside the greenhouse, 

 scrupulous care must be taken with the lamp to 

 see that it is kept clean, or injurious fumes will be 

 given 'i IV. 



Pipes, Joints, and Fittings. The 4" cast iron 

 pipe, that is, a pipe with an inside diameter of 4", 

 is the one generally in use, except it be for large 

 mains and connections, where 6'' pipes are occa- 

 sionally employed. The pipes are generally made 

 in 9' lengths, with one plain and one socket end, 

 for fitting. Wrought iron pipes are rarely seen in 

 the low pressure system. The pipe which conveys 

 the hot water from the boiler is technically known 

 as the " flow," and the one which takes the cold 

 water back again as the " return," pipe. There 

 may be several " flows " and several " returns," 

 according to the size of the house. The "flow" 

 pipe is generally the upper, and the " return " pipe 

 the lower, and in laving them down a rise of y to 

 J" per !)' run is usually allowed, as this facili- 

 tates ease of working. At the highest part of the 

 apparatus there should be a tap or an automatic 

 air vent in the shape of a small tube let into the 

 pipe and curved at the top to keep out dirt. Air 

 is apt to collect in the pipes, and unless given vent 

 will impede or even prevent the circulation of the 

 water. This is technically known as "air locking." 



Top Heating. As a rule, pipes are laid down 

 close to the floor of the house, following the 

 principle that the hot air is pushed up by the 

 cold, or, as it is commonly phrased, rises. Of late 

 years, however, the practice of running a row of 

 pipes usually 3" round under the eaves of the 

 house has come into vogue. It has been tried in 

 the Palm House at Kew with excellent results, and 

 has been found to prevent a good deal of the drip 

 that is so great an evil in winter. 



Amount of Piping. In all cases it is much safer 

 to have too much piping in a house than too little. 

 At least enough must be provided to keep up the 

 requisite temperature without causing the house to 

 smell of fire heat. To calculate the quantity of 

 piping required for any house, Tredgold enunciates 

 the following rule : "To the length of the hothouse, 

 multiplied by half the vertical height, add one and 

 a half times the whole area of glass, and also 

 eleven times the number of doors. The sum will 

 be the number of cubic feet to be heated per 

 minute from the temperature of the external air to 

 that of the house. Then multiply the cubic feet 

 of air to be heated per minute by the number of 

 degrees the house is to be warmed, and the result, 

 divided by twice the difference between the tem- 

 perature of the house and that of the surface of 

 the pipes, will be the feet super, of pipe required." 

 One foot run of 4" piping gives about 1' square of 

 heating surface, since the diameter is to the 

 circumference of a cylinder as 1 is to 3'141(i, 



etc. The fractions may be ignored for a rough 

 calculation. A good practical method for find. 

 ing the amount of piping required is to divide 

 the cubic area of the house by 'thirty for cool 

 houses, by twenty-five for intermediate houses, by 

 twenty for plant stoves, and by fifteen for houses 

 in which hard and early forcing is to be done. 



Making Joints. Various methods of making the 

 joints are in vogue. Packing with red lead ami 

 tow has an advantage over packing with hemp and 

 iron filings, in that it is to a slight extent elastic, 

 and great pressure does not so often mean a burst 

 joint. The most scientific method is, however, the 

 elastic joint, which, briefly, is a rubber ring com- 

 pressed over the joint by iron collars fastened by 

 bolts and screws. Fitting by these joints is also 

 more speedy than in any other way, Portland 

 cement is excellent for stopping a leaking joint. 

 Of the valves in use, the screw valve is better than 

 the half-turn valve, in that it gives 0, greater 

 command over the flow of water, 



Fuel. (.*<; COAL and CORK.) 



Stoking. A small body of bright fire, free from 

 ashes and clinkers, will give off more heat than one 

 double the size that is choked up with dirt. Clean- 

 liness is the secret of good stoking, and with this 

 should be combined an intelligent use of the 

 draught dampers. It is much better to trust to 

 these when making up the fire the last thing at 

 night than to throw on quantities of ashes, as is so 

 frequently done. 



HECHTIA. 



Handsome and distinguished looking plants (ord. 

 Bromeliacea:), usually to be seen amongst collec- 

 tions of succulents. The leaves of all the species 

 are long, narrow, recurving, and possessed of sharp 

 teeth. The plants may be increased by offsets, 

 which are occasionally produced by old plants. 

 They should be firmly potted, singly, in small pots 

 in very sandy soil, with plenty of drainage. Older 

 plants like fibrous loam three parts, cow manure 

 one part, crushed crocks one part, and rough sand 

 one-sixth of the whole. Less water is required 

 than for the majority of plants, and very little 

 indeed should be given in the winter. 



Principal Species : 



argentea, Ivs. 1^' to 2' long in a dense tuft or 

 rosette, silvery. 



Other Species : 

 glomcrata, Ivs. silver on stenopetaln, Ivs. with 



lower surface, grn. on strong triangular spines 



upper (Kyii. Ghiea- (*y. cordyliuoides). 



breghtii). 



HEDERA. (IVY) 



Description. A small genus (ord. Araliaceae) 

 with regard to species, there being only three, but a 

 large one when the immense number of varieties ia 

 taken into account. Hedera Helix, the common 

 Ivy, is perhaps the most important of all the 

 climbing plants that are hardy in this climate. 

 It is distributed naturally over the northern hemi- 

 sphere, and there are few subjects that exhibit so 

 much capacity of adaptation to circumstances. 

 The Ivy has been cultivated for years, and under 

 cultivation has given rise to hundreds of varieties, 

 of which a selection is given on pp. 4(12. lo.'i. 

 Some of the stronger-growing climbers, such as this 

 type itself, the Irish Ivy (canariensis), dentata, 



Ifebei'linittm (tre 

 Jleiloroma (>ve Darminia). 



