NATURAL CONDITIONS OF PLANTS. 9 
the borders of thermal springs. The degrees 
of moisture vary exceedingly. The late Mr. 
Allan Cunningham often expressed to me his 
surprise at the extreme dryness of the atmo- 
sphere and soil in New Holland, where many 
species of plants grew, species, too, which did 
not appear to he constructed like the cactuses, to 
resist extreme drought ; hut there, hanksias and 
acacias would live for months without either dew 
or rain, in soils where not a particle of moisture 
was to he found on digging several feet below 
their roots. Numberless other plants, indepen- 
dently of those which live in water, cannot exist 
unless the atmosphere and soil are saturated with 
moisture — such as Trichomanes speciosum, and 
numerous tribes of plants which adorn the rocks 
in waterfalls, &c. One of the most important 
objects in gardening — but one which is too fre- 
quently overlooked — -is to furnish plants with the 
requisite amount of moisture. That acute ob- 
server, Dr. Hooker, remarks that in Dr. Camp- 
bell’s garden, at Darjiling (Sikkim Himalaya), 
there is a perpendicular bank, fifteen feet high, 
exposed to the west, and partly sheltered from 
the south-west by a house. Rhododendron 
Dalhousice has annually appeared on this, the 
seeds being imported by the winds, or birds, 
from the neighbouring forest ; the seedlings, 
