16 
WATER AND WATERING. 
very long period without access to moisture of any kind, so also 
it differs at times in the same individual according to the season 
or affecting circumstances ; structural variations may serve as a 
key to the requirements of plants in this respect, where anything 
of their physiology is known, as for instance those remarkable 
for coriaceous leaves, and a general indurated or “hard-wooded” 
habit, give off a much smaller quantity of moisture than will be 
observed among soft-wooded plants, or, to be more familiar, a 
Pelargonium will emit a greater proportion of moisture than a 
Heath, and consequently in its cultivation, will require more 
water to be supplied to it than would be beneficial to the other 
plant; the evaporation is found to proceed from the leaves, and 
in proportion to the texture facilitating its escape and the extent 
of surface, so will the amount of moisture range. 
If specimens were taken from each of the great families having 
the same stature or exposed surface, it would be found that her¬ 
baceous plants, or those composed entirely of leaves, emit the 
largest amount of moisture; next to them would be placed the 
suffruticose, to be followed by the ligneous, and at the opposite 
extremity would occur those which are destitute of true leaves, 
as the cacti; and so in the cultural management of a whole year, 
the quantity absorbed would be found to present exactly the same 
ratio. But, as before remarked, the variation of seasons makes a 
great difference in this respiratory action, and here we require 
the geographical knowledge previously mentioned; in our gar¬ 
dens are collected specimens of the vegetation of every known 
part of the world, and what are the agencies by which we are 
enabled to imitate the several climates from which they have in¬ 
dividually been obtained ? Simply, heat and moisture; by the 
judicious increase or diminution of these, we may keep together 
and enjoy in one small spot the products of the four quarters of 
the globe. The application of heat is more readily understood, 
because of its tangible effects on our own persons, but to place 
all these plants together in the open air and expect them to 
thrive, is not more unreasonable than # is the practice of that 
person who would treat them all alike with regard to the other 
agent, moisture, by “watering them when they are dry;” it is, 
in effect, the same, for in either case they are severally expected 
to conform to one climate and one season; such a case, it is true. 
