THE KINGDOM OF FLOWERS 
few instances the same species is com- 
mon to both countries. The most extra- 
ordinary instance of this is Diphylleia 
cymosa (umbrella leaf). This plant oc- 
curs in localities separated by 140 de- 
grees of longitude and shows absolutely 
no marked variation. 
In the instances mentioned above, the 
families are absent from any other re- 
gion in the world. In others—for ex- 
ample, oak, hornbeam, elm, birch, ash, 
etc——where the families range around 
the whole temperate zone of both old 
and new worlds, the individual species 
from China are usually more closely akin 
to those of North America than to Eu- 
rope. 
The explanation is to be found in the 
glaciation of the northern hemispheres 
in prehistoric times. In those far-off 
times the land connection between Asia 
and North America was much more 
complete than it is today, and the flcza 
extended much farther to the north. 
The ice-cap which gradually crept down 
forced the flora to recede towards the 
equator. Water, when the period of 
great cold was over and the ice-cap re- 
ceded, the plants crept back; but the ice- 
cap remained at a more southern latitude 
than before, and consequently rendered 
much of the land formerly covered with 
forests much too cold to support vege- 
table life of any sort. This rearrange- 
ment after the ice age caused a break 
between the two hemispheres and conse- 
quent isolation and cutting off of the 
floras. Other agencies and factors played 
a part, but the above explains briefly and 
roughly why the floras so much alike 
should, today, be so widely separated 
geographically. 
CHINA CAN STILL HELP US ENORMOUSLY 
Since we live in a utilitarian age, in 
all work the question arises as to its 
practical use and value to mankind. 
This botanical exploration work in China 
has something more than a _ purely 
zesthetic and academic value. The beau- 
tifying of our homesteads and parks and 
the additions to our knowledge are not 
1027 
the beginning and end of this work so 
energetically pursued by the Arnold Ar- 
boretum. But as a scientific establish- 
ment, devoted to the study of woody 
plants, its work, after classifying, nam- 
ing, cultivating, and demonstrating the 
hardiness and value of new introduc- 
tions, ends. It is for others to take up 
the commercial side of these plants and 
their economic products. ‘To the nur- 
seryman and plant breeder the potential 
value of these new introductions may 
mean millions of dollars in the near fu- 
ture. The possibilities are incalculable. 
Our Department of Agriculture at 
Washington is alive to the possibilities 
of China as a source of new economic 
plant products, and has already had an 
explorer in the northwest of the Empire. 
In no other country do economic vege- 
table products enter so largely into ex- 
port trade as in China. ‘Take, for ex- 
ample, oil-bearing plants. There are a 
dozen or more largely cultivated in 
China, but the demand exceeds the sup- 
ply. In the matter of drying oil for 
paint and varnish works, Chinese wood 
oil is superior to linseed oil. This oil, 
obtained by crushing the seeds of two 
kinds of small trees, known as Aleurites 
Fordu and A. cordata, is annually ex- 
ported in increasing quantities. The 
former species supplies by far the major 
proportion of wood oil exported. It is 
abundant in the rocky regions around 
Ichang and throughout the Yang-tse 
gorges, thriving on the poorest of soil, 
where a minimum rainfall of 30 inches 
falls, withstands drought and a few de- 
grees of frost. When in flower, which 
occurs before the leaves unfold, it is very 
handsome, and it never fails to produce 
a large crop of its green apple-like fruits. 
There must be parts of this vast country 
of ours where the wood-oil tree would 
thrive, and some day it will probably be- 
come a great industry with us (see page 
1024). 
Every one is familiar with the lacquer 
work of China and Japan. ‘The tree 
(Rhus vernicifera) that produces this 
