VISITS TO NURSERIES. 
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pestilence. The Cactece, and their allies, which are plants that 
are endowed by nature with powers of absorbing moisture by a 
surface which appears to be proof against all waste by evaporation, 
even when the rays of a vertical sun are mouldering the rock, and 
scorching the sand, appear in numerous array. The collection of 
Mammillarias is large and well arranged. To these follow the 
Melocacti, and Cacti properly so called ; and this part of the col¬ 
lection closes with the Mesembry anthidce and the Eujohorbice. 
In this section, of which the greater part are seen at one glance, 
we have the vegetation of some of the most singular surfaces in 
tropical climates. They grow on the sandy expanses, on the tops 
of walls and houses, in the crevices of rocks, and in other situa¬ 
tions, where nothing analogous to what we call vegetable mould 
is to be met with. Notwithstanding this, they grow with great 
vigour according to their habit, and clothe the dry sand or naked 
rock with an abundant though peculiar vegetation. The forms of 
all of them are peculiar, though many are allied to our goose¬ 
berries in their natural characters, and even in the flavour of their 
fruit. The flowers of many of them are of exquisite beauty, so 
that, with all their singularity, they are highly ornamental to those 
places where they are abundant. They merely adhere to the 
ground, as the E'pijphytce of the tropical forests adhere to the stems 
of trees ; and like these they appear to draw the whole of their 
nourishment from the atmosphere. Plants which do this are 
especially worthy of study, as throwing light on the very obscure 
and indeterminate subject of the food of plants, respecting which a 
question has often been raised, but never satisfactorily answered. 
Very many of those general principles of vegetation, an accurate 
knowledge of which is essential to the successful cultivation of 
every species of plant, and especially to the art of obtaining flowers 
of the best description and in the greatest abundance, may be 
learned from the study of such a collection as that at Kew. Into 
the particulars of these we cannot of course enter, but must leave 
every visitor to find out his own lesson and profit by it. One thing 
however we may mention with regard to many of the trees of the 
southern hemisphere, as contrasted with those of the northern. 
In the latter, the turpentine and other resins and gums are found 
in the timber of the tree, and they remain there, and, as it were, 
embalm the timber ; so that it lasts long after it is cut down and 
applied to useful purposes. In some situations, however, those 
