BOTANICAL GEOGRAPHY 331 
trees on ascending a mountain is well shown in Fig. 234. 
The treeless character of the mountain summit is also 
plain. 
Recent experiments have shown that many ordinary 
plants promptly take on alpine characteristics when they 
are transferred to moderate heights on mountains. For 
instance, a rather 
commonly culti- 
vated sunflower,? 
when planted at a 
height of about six 
thousand five hun- 
-dred feet, instead 
of having a tall 
leafy stem _ pro- 
duces a rosette of 
very hairy leaves 
lying close to the 
ground, thus _be- 
coming almost un- 
recognizable as a 
sunflower. The 
change was even 
greater than that 
shown in the rock 
rose (Fig. 235) cultivated by the same experimenter. The 
A, low ground form ; B, alpine form. 
peculiarities of alpine plants appear to be due mainly to 
the intense light which they receive during the daytime, 
1 Part of the diminution is only apparent, — the effect of distance, — but the 
growth at the highest levels is often less than waist high. 
2 Helianthus tuberosus, the so-called Jerusalem artichoke. 
