INTRODUCTION. 
hollow behind the rocks. Cavities full of air are death to roots, 
accumulate damp, and make homes for mice. 
A very important luxury comes in at this point, if the builder 
can contrive or afford it. This is the underground water-pipe. 
All alpines respond (if their drainage is perfect) m the most 
marvellous way to underground waters, which remind them of 
the percolating snows far down in the soaked mountains into 
which their pertinacious toes are plunged. Not only are their 
roots thus kept cool and happy, but the prevalent moisture tran- 
spires through the surface soil and forms an aureole of coolness 
round the plants, protecting them against the arid furies of the 
sun. Overhead watering, on the other hand, though better than 
nothing, is not nearly so popular among plants in general, and 
even less so than usual among alpines. Therefore no pains should 
be spared in securing an adequate supply of water underground. 
A pipe should be connected with a standing water-cock, and run 
through the top of the mound or bank, about twelve inches down 
in the ground; it should then have minute perforations made in it 
alternately, on either side, at intervals of six or nine inches. The 
soil should then be filled in, the compilation stocked with its 
plants, and the water turned on. If possible, it may run steadily 
from April to the end of September, after which it should be turned 
off till the end of the following April. If, however, this full flow 
cannot be achieved, at least the stream should run for two half- 
days in the week, or one whole day. Even this, of course, is an 
unattainable counsel of perfection to many an earnest soul; these, 
however, still have it in their power to secure the underground 
moisture that their treasures desire. Let them sink large flower- 
pots along the top of their bank or mound (or drain-pipes driven 
straight down), and then, at intervals, fill these up with water, 
which will thus permeate the depths and please the plants. 
Smaller pots may even be sunk, behind and above special rari- 
ties, such as the Arctic Andromedas or Androsace alpina; and 
the pit shafts thus formed may easily be masked by ferns or 
stones. 
So much, then, for the main mass of the rock-garden. 
XXXIV 
