MOUNTAIN OR ALPINE VEGETATION 



487 



The gradual diminution of the height of the trees on ascend- 

 ing a mountain is well shown in Fig. 3 7 1. 1 The treeless charac- 

 ter 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 com- 

 monly cultivated sunflower, 2 when planted at a height of about 

 sixty-five hundred 

 feet, instead of 

 having a tall, leafy 

 stem, produces a 

 rosette of very hairy 

 leaves lying close to 

 the ground, thus be- 

 coming almost un- 

 recognizable as a 

 sunflower. The 

 change is even 

 greater than that 

 shown in the rock 

 rose (Fig. 372) culti- 

 vated by the same 

 experimenter. The 

 peculiarities of alpine 

 plants appear to be 

 due mainly to the in- 

 tense light which 

 they receive during the daytime, 3 to the strongly drying char- 

 acter of the air in which they grow (due partly to its rarefaction), 

 and to the low temperature which they must endure at night. 



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. 



8 The experiments of Professor Frederic E. Clements on Pikes Peak, 

 however, seem to show that light is not a principal factor in the production 

 of alpine characteristics in plants. 



FIG. 372. Two plants of rock rose (Helianthemum) 



A, low ground form; B, alpine form. Both drawn 

 to the same scale 



