230 
HISTORY OF BRITISH FERNS. 
used among the rock work may have in addition a portion 
of the sandstone pounded and intermixed with it. That 
used for inundatum in the lower part of the case will not 
require this intermixture, and, in fact, will be the better 
as it approaches the unctuous texture just referred to, 
which the presence of a good supply of water will soon give 
to it. 
All parts of the soil should be kept rather moist than 
otherwise, by the application of fresh water occasionally; 
but as the confinement of the atmosphere in the damp state, 
in a close case, might tend to produce decay in some parts 
of the vegetable tissues, the little door or hinged sash may 
from time to time be left open for a few hours, in order 
that the stagnant moisture maybe carried off, when afresh 
supply will be doubly grateful to the plants. 
It must be recollected, that the soil will be exposed to 
very slight drying influences, and can, therefore, never 
require to be very copiously supplied at any one time ; the 
proper course being, rather to ventilate frequently, say 
once a week, in order to carry off the accumulated damp¬ 
ness, and then by a moderate fresh supply to produce a 
continued change of the watery element. For the same 
reason, and to prevent the souring of the soil, which always 
