ROCKS AND ROCK-PLANTS. 
89 
number, even amongst plants that are quite hardy enough to endure several 
degrees of frost ; and to some of our native species, which, when favourably- 
situated at the roots, will brave the sternest winters in the most exposed localities; 
of which the rock-rose (Heliantkemum) is a familiar example. And here we may 
remark, en passant, that in all cases where this family are cultivated in common 
flower-beds, they must not only be well drained at the roots, but the surface 
should be covered with small pebbles, shells, or pieces of brick, to prevent the 
shoots from resting directly on the damp earth. Of course, on the side of a hill 
where they are exposed to brisk winds, and more in their natural circumstances, 
they are not so liable to harm without the pebbles, as in low or level situations. 
Decided succulents, such as Sedums, Sempervivums, and the hardier species of 
Cacti in summer, together with the whole race of alpines, are rarely so successfully 
managed in the open garden in any other way, as in situations similar to that we 
are now advocating. 
We have occasionally seen very engaging effects created by masses of the 
common scarlet Pelargonium planted on a pile of rough stones, having the inter- 
stices filled with mould, Under these circumstances, the excessive luxuriance of the 
species is held in check, and a more speedy and copious bloom unfolded. Petunia, 
Nolana, Salvia, Amphicome arguia acquire an earlier and a more floriferous habit. 
The Mesemhrya n them um tricolor (or M. pyropmum, as it is also called) is a 
delightful object when cultivated thus, in extensive patches ; and the contrast of 
tint which stones afford in a natural state — -that is, worn with time, and not 
presenting any recent clefts — is a great enhancement ; through lending a more 
decided character to the colours and appearance of the flowers and foliage, without 
being, in the smallest sense, destructive of harmony. 
We might multiply instances almost beyond number of beautiful things that 
are benefitted by the kind of situation here broached but our object is rather to 
draw attention to its influence generally than to individualise farther than is 
necessary to the explanation of the subject, and to indicate the kind of plants 
which are capable of a more exalted character, or extensive culture beneath its 
working. 
We have yet to invite deliberation specifically to its adoption in the narrow 
borders attached to the front of those plant-houses having a low parapet wall, with 
a view to their amelioration and increased adaptability for the reception of stove 
and the more tender greenhouse exotics. Few, we imagine, will attempt to 
gainsay the desirableness of extending the cultivation of such plants as the 
Achimenes coccinea, the delicate Thunbergias, Alstrcemerias, and similar attractive 
things, amongst which we may include a vast number of species belonging to the 
Amaryllis and Iris tribes ; and these can be made to grow and flower favourably 
in similarly protected places to those we have just alluded to. 
In addition to what has been already advanced as influential in augmenting 
the power of a delicate exotic to exist and flourish in the open air, we must. now 
VOL. XII. NO. CXXXVI. N 
