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 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 
Fic. 260. VERTICAL SECTION OF 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, 
au every case, it is necessary that the Boiler should 
fixed in a proper rit | It is also good policy to have 
Boilers about 30, or Sie | per cent., more powerful than 
is actually required, when they are new, as, from various 
nee ay Ue heating: tg le off in a year or two 
desirable to. stimulate’ the action in order tor 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- 
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 and Stoking. 
BOIS-PERDRIX. See Heisteria. 
‘BOLBOPHYLLUM. See Bulbophyllum. 
BOLETUS (from bolos, a mass; in reference to its 
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. Itis easily distinguished, and is often of large size 
and somewhat unshapely; the pileus is usually of a dusky 
= ALN RI ALU Vir L 
— NR soi fi N. ; ee a 
Fia. 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 e 
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. 
BOLEUM (from bolos, a ball; in reference to the shape 
of the seed-pods). ORD. Orucifere. 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 
mee a * A. cream-coloured ; racemes erect, elon- 
B. asperum Cone" shiort, the lower ones bracteate. April. 
e Alternate, oblong, linear; lower ones somewhat divided. 
~À suffruticose, erect, branched plant, hispid from stiff hairs. 
h. 6in. to lft. 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. a 
