4 
NATURAL CONDITIONS OF PLANTS. 
and more or less abortive. Wlien we survey 
tbe vegetation on the surface of the earth, we are 
struck with the endless diversities of form which 
present themselves to our astonished gaze, from 
the magnificent palms of the Tropics and the 
bread-fruit of the Polynesian Islands to the rein- 
deer moss of Lapland, or the red snow of the 
Arctic regions. Yet the growth of all is governed 
by immutable laws, and they owe their varying 
forms to varying climatal conditions. 
In Rome upon Palm Sunday 
They bear true palms, 
The Cardinals bow reverently 
And sing old Psalms : 
Elsewhere their Psalms are sung 
’Mid olive branches. 
The holly bough supplies their place 
Among the avalanches : 
More northern climes must be content 
With the sad willow, — Goethe. 
HEAT. 
The heat to which plants are subjected varies 
from 30° or 40° below zero to 170° or 180° Fahr. 
In Spitzbergen, the earth in the middle of the 
short summer is never thawed to more than the 
depth of a few inches, and the stem of the only 
tree, a little willow, if tree it can be called, runs 
under ground for several feet within an inch or 
two of the never-melting ice, whilst in Mexico 
