on a sunny rockery out of doors, it will be found a wise precaution to
place either a pane of glass or a handlight over the plants in wet
autumns and during winter, not so much to serve as protection from cold
as to shield them from an excess of moisture at a time when it would
prove injurious.

Temperature.--As the amount of heat required by the different species
of Cactus varies very considerably, and as the difference between the
summer and winter temperatures for them is often as great as it is
important, it will be as well if we mention the temperature required by
each when describing the species. It is true that the majority of
Cactuses may be kept alive in one house where all would be subjected to
the same temperature, but many of the plants would merely exist, and
could not possibly flower. It would be easy to point to several
instances of this unsatisfactory state of things. At Kew, for example,
owing to the arrangements necessary for the public, it is found
convenient to have the majority of the large collection of Cactuses in
one house, where the plants present an imposing appearance, but where,
as might be expected, a good number of the species very rarely produce
flowers. The Cactuses which inhabit the plains of the Southern United
States are subjected to a very high summer temperature, and a winter of
intense cold; whilst on the other hand the species found in Central and
South America do not undergo nearly so wide an extreme, the difference
between the summer and winter temperatures of these countries being
generally much less marked. A word will be said under each species as to
whether it is tropical, temperate, or hardy, a tropical temperature for
Cacti being in summer 70 degs., rising to 90 degs. with sun heat, night
temperature 60 degs. to 70 degs., in winter 60 degs. to 65 degs. Temperate:
in summer 60 degs., rising to 75 degs. with sun heat, night 60 degs. to
65 degs., in winter 50 degs. to 55 degs. The hardy species will, of course,