PLANTS IN ARCTIC-ALPINE ENVIRONMENT — SHETLER 487 

 THE TUNDRA FORMATION — AN ECOLOGICAL LOOK 



Our attention is drawn first to the general physiognomy or structure 

 of the vegetation — the "gross anatomy," if you will, of the tundra 

 vegetation. Closer examination w^ill bring us secondarily to the 

 nature and composition of the individual plant communities. 



Every mature plant has a particular habit or shape and mode of 

 growth that we call its "growth-habit" or "growth-form." It may be 

 woody or herbaceous, tall or short, erect or prostrate, bushy or f astig- 

 iate, annual or perennial, etc. Growth-form may vary greatly 

 within the same species and habitat; yet there is a distinct tendency 

 for the members of a given species, sometimes of a whole genus or 

 family, to fluctuate around an average highly characteristic form. 

 This more-or-less stabilized, presumably growth-form is called the 

 "life-form" of the species. (Some species encompass more than one 

 race, and the races may have different life-forms.) It represents a 

 long-term genetic compromise with the environment. Raunkiaer 

 called the life- form a "biological type." 



Various systems have been devised for classifying plants according 

 to their life-form. The ancient Greeks already used the obvious dis- 

 tinctions between trees, shrubs, and herbs to classify plants. In 

 modern times, a more refined system has been proposed by the late 

 Danish botanist Raunkiaer, based on the position of the "perennating" 

 (renewing) bud. It has been variously modified by other authors, 

 but the usual classes are essentially Raunkiaer's : 



1. Phanerophytes. — Renewal buds on shoots at least 25 centimeters 

 above the surface of the ground ; mostly trees or shrubs. 



2. Chamaephytes. — Renewal buds on shoots between ground-level 

 and 25 centimeters high ; perennial herbs and some undershrubs. 



3. Hemicryptophytes. — Renewal buds at ground level or within the 

 surface layer of the soil ; perennial herbs. 



4. Geopliytes. — Renewal organs (bulbs, tubers, rhizomes) well bur- 

 ied in the soil ; biennial or perennial herbs (subclass of Ciyptophytes). 



5. Hydrophytes. — Water plants, whether anchored to the bottom or 

 not, except free-floating or swimming types ; tends to cut across other 

 types and is often omitted (subclass of Cryptophytes) . 



6. Therophytes. — Annuals, completing entire life cycle in a single 

 growing season, surviving unfavorable periods as seeds or spores. 



Raunkiaer used this system to derive life-form "spectra" for various 

 floras, as a whole, converting the number of species in each of the life- 

 form classes into a percentage of the total sample. As a standard, he 

 developed a so-called "normal spectrum," based on 400 species chosen 

 more or less at random from the world's flora. Then he was able to 

 deduce, for example, whether a tropical flora had more or less thero- 

 phytes than an arctic flora, etc. Some general observations were : (1) 



