134 
ON THE INFLUENCE OF CLIMATE ON PLANTS. 
the whole tribe of Cactce, but there are some species which will bear exposing to 
the open air during certain periods of the year ; such, for instance, as Cereus 
speciosissimus^ speciosus, Jenkinsoni% and others of similar habits, and if these are 
annually placed in an exposed situation in the open air, after they have ceased 
growing, they will be found to flower much more abundantly, and in far greater 
perfection, in the succeeding year. Throughout the whole season, and at all stages 
of the growth, they should constantly receive as much solar light as can be dispensed 
to them, except during the short period they continue in flower, when they may be 
placed at a farther distance from the glass, to preserve them in flower for a greater 
length of time. The variation of temperature and moisture which these plants 
require, will form the subject of future articles, and we now proceed to off*er a few 
observations on the efi'ect of light on the numerous species of Mesemhryanthemum. 
The extensive and interesting genus just named, with the exception of the genus 
Erica, contains a greater number of beautiful species than any other with which 
we are acquainted, and there is not an individual species of it but is more or less 
ornamental. It is generally believed, that if these plants are placed in a poor and 
sterile soil, they may be induced to flower more profusely, and that the flowers will 
be finer and of better colours. To a limited extent this notion is correct, but it is 
a great error to suppose that this treatment will of itself be sufficient to produce 
the efi'ect above mentioned. It is also imagined, that, by withholding water from 
these plants for a time, their flowering may be facilitated, and tlie flowers rendered 
finer and more abundant ; this is likewise to a great extent an equally erroneous 
hypothesis, if the success be attributed to this treatment alone, as may be suffii- 
ciently proved by placing the various species of this genus in a sterile soil, adminis- 
tering water very sparingly or wholly withholding it for a time, and keeping them 
in a shaded or gloomy situation where the rays of the sun can never reach them ; 
the result of which will be, that they will either produce few and insignificant 
flowers, or be altogether destitute of them. But if, instead of being kept in this 
unfavourable position, they are placed in an open exposed situation, where they 
can receive a great degree of solar light, they will speedily produce a most brilliant 
display of flowers, and these will continue expanding for a great length of time. 
It therefore plainly appears that it is the injlimice of light which causes these plants 
to flower so profusely, and not the nature of the soil or the quantity of water 
administered ; though these latter doubtless contribute in some degree to produce 
the above desirable effects. Indeed, this must be abundantly evident to every 
intelligent cultivator who has been accustomed to place these plants in the open air ; 
for it is irrational to suppose that poverty of soil or scarcity of water alone would 
cause them to flower so freely. Mesembryanthemums, then, like most other succu- 
lent plants, require a great intensity of solar light to enable them to produce their 
flowers in perfection ; and whether they are kept in the succulent house, or placed 
in the open air, this important particular should be duly and properly attended to, 
otherwise no success will be attained. During the summer months, however, many 
of the species will flower better in tlie open air than if kept in the succulent house, 
