1174 ARBORETUM AND FRUTICETUM. PARD Ast. 
reader will bear in mind, differs from an ericetum, in containing all the plants 
of the order Ericacez, while an ericetum, or heathery, is limited to the 
species of the section Hricez normales. 
All plants which require peat soil do so in consequence of their having 
hair-like roots; and, in the culture of the ligneous Fricacez, as of all plants 
whatever in peat soil, to insure success, it is essentially necessary to keep the 
soil in an equable degree of moisture. The reason is, that plants having hair- 
like roots never extend these to any great distance from the stem, or main 
root; and, consequently, that they draw their nourishment, or what, in a 
practical sense, is equivalent to it, their moisture, from a very limited space. 
Hence, no plants suffer more from drought than the Hricacez, whether in 
the open air in beds, or in the green-house in pots; and no plants are more 
difficult to recover after they have sustained injury from being kept too dry. 
Hence, in very hot summers, the rhododendrons, azaleas, and other shrubs 
of this order, which grow in common garden or shrubbery soil, are frequently 
killed to the ground, without shooting up again the following year, as is the 
case with the shrubs of most other orders, killed down by drought, Every 
American garden, therefore, ought to be laid out in some situation, and, ac- 
cording to some principle, not only favourable to the retention of the natural 
moisture of the soil, but also favourable to the application of moisture arti- 
ficially. A level surface at once supplies both the conditions to a certain 
extent; and a level surface, sunk 5ft. or 6 ft. below the surrounding surface, 
supplies both in the most perfect manner. The advantage of placing an 
American ground in an excavation some feet under the surrounding surface 
is, that the soil in the excavation will always be moister than that of the sur- 
rounding surface, in proportion as the one is lower than the other. The soil 
in such an excavation will also be found cooler than that of the general sur- 
face, though both may be alike exposed to the direct rays of the sun. These 
results may not at the first sight appear obvious; but they take place in con- 
sequence of temperature and water having both a continual tendency to 
come to a level. 
An ericacetum ought, therefore, to be laid out in an excavation, the sur- 
face of which is reduced to a perfect level, in order to gain all the advantages 
of moisture and coolness which the natural situation affords : and, to admit of 
supplying water artificially to the soil in the beds in the most economical 
manner ; and, at the same time, in the manner best adapted for the plants, the 
excavation should be intersected with drains at regular distances; all these 
drains communicating with a main drain in the centre, and this main drain 
communicating with the source of the water, which should be so arranged as 
to be turned on and turned off at pleasure. The drains may be laid out in 
parallel lines, 10 ft. or 12 ft. apart, and 2 ft. or 3ft. under the surface; and 
they may be formed of bricks, laid without mortar, 9 in. deep, and 43 im. wide. 
The main drain in the centre, with which they communicate, may be a foot 
wide, and a foot deep. The bottom of all the drains ought to be on the same 
level. The water may be admitted to one end of the main drain by various 
means. If conveyed under ground in a pipe, that pipe should be 3 ft. or 4 ft. 
under the surface, so as not to be injured by frost ; and the stopcock may be 
reached from the surface through a vertical shaft of 2in. or 3 in. in diameter, 
formed by brickwork, and closed at the surface by a brick or stone, so as not 
to appear unsightly. If the water is supplied from a pump on the spot, that 
pump need not lift the water higher than the upper surface of the drain; and 
it may easily be contrived with a removable handle, so as to have no appear- 
ance of a pump, except when it is in use. Where the water is supplied 
by water-carts, or from a pond at a short distance, it is only necessary to pour 
it into the main drain through a funnel carried up in masonry or brickwork 
to the surface, from the centre of the main drain, having a stopper of brick or 
stone to put on when not in use. 
Water may be supplied artificially to an ericacetum by surface drains ; but 
these will not apply so well as under drains, in cases where the garden con- 
