IvEW GARDENS. 
169 
and thought of the director and assistant-director has been 
absorbed by their colonial correspondence, and in questioning 
and answering the questions of their colonial visitors. 
Statistics of Plants as Classified according to their 
Cultural Requirements. 
If we classify plants according to the garden treatment 
they require, they fall into four main groups : the inter-tropical 
zone includes a land area of 40,000,000 square miles, and the 
total number of characteristically tropical plants known to 
science may be roughly estimated at 40,000 or 50,000. These 
are provided for at Kew in the Palm House, the Tropical Fern 
House, the Aroid House near the main gates, the central 
portion of the new range, and various small propagating 
houses, which are not open to the public. Of course the 
expense incurred in cultivating in the English climate any 
plant of this group is considerable, so that a careful selection 
from the 40,000 or 50,000 species has to be made. 
The second group of plants consists of those that can 
bear the English summer, but need protection during winter. 
These are provided for at Kew in the Temperate House, the 
Succulent House, the cool Fern House, and the cooler parts 
of the new range. To this group belong the members of the 
three rich floras of the south temperate zone, where the 
height of summer corresponds with the depth of our north 
temperate winter. To this group belong about 80,000 species, 
or about a third of the plants that are known. 
Next come the hardy plants. The north temperate zone 
occupies about one-tliird of the earth’s surface, and its plants 
number 20,000 species. Of these at Kew the classified 
collection of the herbaceous types is contained in what is 
called the Herbaceous Ground, which is just north of the 
Cumberland Gate. Here are grown about 2,000 perennials and 
a thousand annuals, arranged under their respective orders. 
The classified collection of shrubs and trees is scattered 
over the different parts of what was formerly called the 
Pleasure Ground. For the special growth of Alpine plants 
two rockeries have lately been laid out. The total flora of the 
Arctic zone does not reach 1,000 species, and the plants which 
are confined to the higher levels of the mountains of the 
north temperate may perhaps be twice as numerous, in all 
3,000 species of what gardeners call “ Alpines,” plants 
specially adapted to a cold damp climate with a short summer. 
If we attempt to classify the plants of the British possessions 
under these four climatic groups, the result will be something 
like this :— 
