PLANTS IN ARCTIC-ALPINE ENVIRONMENT — SHETLER 491 



with latitude. In themselves, altitude or latitude are not significant 

 of course, but only as indices of a changing environment. 



These two examples illustrate the biologist's perennial dilemma 

 when he tries to translate correlation, in this case statistically signifi- 

 cant, into something of biological significance. The negative height 

 correlation is quite general and well known m plants; we expect plants 

 to get shorter as we go toward arctic or alpine areas, because of the 

 more rigorous environmental conditions, already discussed. I am 

 simply saying statistically here what we have already stated earlier — 

 arctic-alpine plants tend to be dwarfed. On the other hand, the tend- 

 ency for the harebell flowers to get larger with increasing altitude or 

 latitude is not as general a tendency, and the biological significance of 

 this trend is more equivocal. Perhaps the larger flowers compensate 

 for the fewer insects in this environment; their greater size might 

 have greater attracting power. Certainly, insect-pollinated species, 

 such as the harebell, must attract insects to reproduce successfully, 

 and a reduced insect density is a handicap. Not all the insect-polli- 

 nated species have large flowers, however, and it would be misleading 

 to conclude that pollination relationships explain the larger flowers 

 in the arctic-alpine environment satisfactorily. Wliatever the reasons, 

 nevertheless, the correlation is often noted that arctic-alpme species 

 tend to have large showy flowers (pi. 9, fig. 2) . 



The well-known tendency of arctic-alpine plants to become dwarfed 

 suggests to us what might be the only important generalization that 

 can be made, namely, that there is in the arctic-alpine environment 

 an overall trend among the plants toward the reduction of surface 

 area. Dwarfing has the effect of reducing the amount of exposed 

 shoot, including stem, branches, leaves, and inflorescence. The above- 

 ground stem may be virtually nonexistent, or if present it may creep 

 along the surface of the ground. Grasses and sedges, both very 

 successful in the arctic-alpine environment, have subterranean or 

 partially superficial creeping stems; the same can be said for the 

 willows. Dwarf willows, for example Salix phWbophylla Anders. 

 (pi. 5), provide superb examples of this tendency. In all their re- 

 productive features they are perfectly orthodox willows, yet their 

 vegetative parts are so reduced that those familiar with only temperate 

 willows are prone to be taken aback by their first experience with 

 these arctic-alpine dwarfs. They have in effect done away with 

 every vegetative flourish that the life cycle could spare, retaining 

 little more than the inflorescence above ground. Such is true of 

 arctic-alpine plants generally, which fact impresses one time and 

 again as he moves about in tundra regions (pi. 9) . 



The reduction-of-surface-area trend can be observed in the very 

 form and structure of the plant organs of many plants. The leaves 

 are often more or less in-rolled (revolute), leathery, and hairy on 



