198 



THE DICTIONARY OF GARDENING, 



Boilers continued. 



of the Boiler, has to be considered, should such a contin- 

 gency occur, it is certainly advisable to reduce all risks 

 to a minimum ; and as the average life of a Boiler is from 

 ten to fifteen years, a slightly larger first cost is not of 

 very serious moment. The forms of Boilers are very 

 diverse, and, in some of the patented forms, complicated. 

 But, whatever the shape, the following points are essential : 

 A clear and unrestricted waterway of not less than 2in. in 

 thickness ; the greatest exposure of surface to the direct 

 action of the fire ; a sufficient fire space ; and a fire-bar 

 area calculated to supply enough fresh air to the fire to 

 support thorough combustion. The forms generally used 

 for horticultural work are the following, or some modifi- 

 cations of them; and, however grand the name, their 

 chief value consists in the attested heating capacity 

 at a given cost: The Saddle Boiler, which is made of 

 various sizes, with or without check ends, cross tubes, 

 and other devices for increasing the heating surface, and 

 also of a tubular form; the Upright Cylinder (a vertical 



FIG. 260. VERTICAL SECTIOW OK CYLINDER BOILER. 



A A, Wrought-iron Boiler, the shaded space showing the Water- 

 way ; B, Ashpit inside the cast base of Boiler ; C, Fire-bars ; D, 

 Flue ; E, Domed Top'; F, Feeding Lid ; G, Flow, and H, Return 

 Pipe Sockets. 



section of which is shown in Fig. 260); the Upright 

 Tubular Cylinder ; the Horizontal Tubular ; and the Cornish 

 or Horizontal Cylinder. Combinations of the various forms, 

 and complicated patterns of different kinds, are made for 

 particular purposes ; but in no case should large Boilers be 

 used, unless they are recommended, by one competent to 

 judge, as suitable for the purpose they are needed to 

 fulfil. In every case, it is necessary that the Boiler should 

 be fixed in a proper manner. It is also good policy to have 

 Boilers about 30, or even 50 per cent., more powerful than 

 is actually required, when they are new, as, from various 

 causes, their heating power falls off in a year or 'two 

 in many places; and, under ordinary work, it ia not 

 desirable to stimulate the action in order to command 

 sufficient heat. There is no doubt that, for general pur- 

 poses, some modification of the Saddle or Cylinder Boiler 

 is by far the best, all things duly considered; but it is 

 impossible to give any practical advice without a thorough 

 knowledge of the requirements of any particular place. 

 Gas Boilers are also useful for small places. These are 

 made in many forms, and are, as a rule, in the shape of a 

 cylinder, with a coned inside, against which the flames 

 play. Some Gas Boilers have also a superheater attached ; 

 this exhausts the heat from the air which has passed 

 through the Boiler. Another good form is made of hori- 

 zontal tubes, which contain the water, the flames playing 



Boilers continued. 



over and amongst them. An atmospheric burner of 

 approved construction should be used where gas is the 

 heating power. A sufficient supply of gas should be 

 assured by using supply pipes of a good size. Care should 

 be taken to keep these pipes free from water, and pro- 

 tected from frost by silicate cotton lagging, or some other 

 good non-conductor. Except for very small places, how- 

 ever, gas apparatus is almost useless, and will never super- 

 sede fuel Boilers. For other particulars regarding Boilers, 

 see Heating 1 and Stoking. 



BOIS-PERDRJX. See Heisteria. 



BOLBOPHYLLUM. See Bulbophyllum. 



BOLETUS (from bolos, a mass; in reference to ita 

 massy or globular form). ORD. Fungi. The only species 

 of this rather large genus demanding mention is B. edulis 

 (see Fig. 261), which is considered an excellent article of 

 food. It is easily distinguished, and is often of large size 

 and somewhat unshapely; the pileus is usually of a dusky 



FIG. 261. COMMON BOLETUS (BOLETUS EDULIS). 



yellow or brownish hue, but sometimes brighter and more 

 of a chestnut colour ; the flesh is white, and does not change 

 to a blue colour when cut (this is a very important cha- 

 racteristic, and should always be noticed). It is a species 

 common in most districts, usually growing in woods, and 

 appearing chiefly in the autumn. 



BOIiBUM (from bolos, a ball ; in reference to the shape 

 of the seed-pods). ORD. Cruciferce. An ornamental, hardy, 

 evergreen shrub, well adapted for rockwork, in ordinary 

 soil. It requires slight protection in winter if planted in 

 very exposed situations. Propagated by seed, sown in a 

 pot, in spring, and placed in a frame, or in the open border 

 during summer. 

 B. asperum (rough).* Jl. cream-coloured ; racemes erect, elon- 



fted; pedicels very short, the lower ones bracteate. April, 

 alternate, oblong, linear; lower ones somewhat divided. 

 A suffruticose, erect, branched plant, hispid from stiff hairs. 

 h. 6in. to 1ft. France. 1818. 



BOLLEA. See Zygopetalum. 



BOLTED. A term used in reference to plants that 

 have prematurely run to seed. 



BOLTONIA (named after J. B. Bolton, an English 

 professor of botany). ORD. Composite. A genus of rather 

 pretty hardy herbaceous perennials. Flower-heads with 

 white or purplish rays. Leaves pale green, lanceolate, 

 sessile. They thrive in common garden soil. Propagated 

 by divisions of the roots, in March. 



