88 
ROCKS AND ROCK-PLANTS. 
I 
by such an appendage ; and in numerous instances wliere it is necessary, or at al 
events, extremely useful and convenient to have cisterns or small reservoirs i; 
various parts of the grounds, they maybe rendered very interesting by surroundin, 
them with an irregular sloping bank of rock, adorned with showy trailing specie 
of plants. 
We have before alluded to the propriety of selecting smaller pieces of stoiK 
and it is quite as desirable to make choice of various sizes. Such also as preser 
a rough uneven surface, and differ most widely from each other in general outlim 
are to be preferred before those with a plain surface. The cliinks and crannie 
between them, and every favourable recess which they afford, should be partialll 
filled with soil for the plants to take root in, adapted to the predilections of th 
species intended to occupy the several stations. In this manner fragments of roc 
may be piled up to a considerable height against steep banks, or employed to hid 
a wall, with propriety ; and the special adaptability of such a spot for the displa 
of trailing plants is by no means of trifling moment. Steep banks of this kind, t 
formed entirely of rough stones run together, will frequently be beneficial, „ 
thrown up, with a view to shut out some unseemly object, or to check a currei 
of wind in some exposed locality. 
But beyond the benefit conferred of supplying a place when the elegance ( 
prostrate species is more apparent, it is also the means of imparting a more matui 
and flowery state with greater certainty than can be gained in some delicate plan 
by other means. Many species, which are constitutionally too tender for tl 
ordinary climate of this country, are induced to grow here with singular prosperit; 
even although in the common flower-beds they will scarcely retain life. It wi^ 
be naturally asked, how is this ? In a great measure it is evidently to be ascribe" 
to the greater uniformity of moisture. In a dry season a plant in a bed of commc 
earth is liable to suffer from a deficiency of moisture, whilst in a wet season it 
equally subject to be injured by a contrary excess. But planted on rocks || 
enjoys a happy medium : the superabundance of fluid percolates amongst, an! 
drains away between the stones ; and if a time of drought follow, the ston| 
prevent that rapid evaporation which inevitably takes place when the soil has r 
such protection. Any one may convince himself of the truth of the latter, and 
its profit to vegetation, by noticing the herbage round a stone in a pasturage i 
corn-field in a dry summer, like that of 1844. L 
A redundancy of moisture in the soil, particularly under a still atmosphere, 
undoubtedly the main cause to which the sudden loss of many species of annuaj 
and delicate-rooted half-hardy perennials, is truly referable. We allude princ 
pally to such plants as Brachycome, Leptosiphon, Zinnia^ Salpiglossis, Phil 
Drummondi and Ipomopsis picta^ amongst annuals and biennials ; and to some ] 
the small Lobelias and Nierembergias amongst perennials ; and even the herbaceov 
Calceolarias and the rampant-growing Petunias are not entirely exempt fro; 
^‘damping off” under the same influence. In wdnter it is destructive to a still greatr 
