38 VEGETATION IN COLORADO-HOLM. [Mem0IRS [Vol T, STx l 



line; a corresponding variation, caused by change of environment at different altitudes, is 

 known from many other Carices, so excellently described by N. J. Andersson. 2 



The caespitose growth is also characteristic of many Alpine species of the Dicotyledones 

 and is sometimes accompanied by another feature, the persisting primary root. But we meet 

 here with several very distinct types. The vegetative organs above ground consist of numerous, 

 often profusely branched, stems with the leaves imbricated or forming flat rosettes at the apex 

 of the shoots; in both cases the specimen represents the structure known so well from Alpine 

 and Arctic plants, resembling a cushion. The primary root may persist for several years as a 

 slender deep taproot, or it may increase very considerably in thickness, and persist for many 

 years; or finally the primary root may die off and become replaced by a fascicle of secondary 

 roots proceeding from the lowermost stem parts. A very simple case of this structure may be 

 seen in Androsace subumbellata (pi. 3, fig. 23). The primary root is very slender, and branches 

 freely; the foliage consists of several small rosettes borne upon a corresponding number of 

 axillary shoots, terminated by inflorescences. When the fruit has matured, the internodes of 

 the inflorescence die off, and a new set of shoots become developed from the axils of the rosette 

 leaves; in Androsace these shoots develop flowers in the first season; in most other plants 

 showing this structure the shoot is a mere vegetative rosette during the first season, the inflo- 

 rescence appearing in the second year. 



A similar structure recurs in Eritrichium argenteum (pi. 4, fig. 30), but the leaves are imbri- 

 cated, since the internodes are extremely short. The Arctic E. villosum Bunge. shows exactly 

 the same structure. In Silent acaulis, Arenaria Fendleri, and Phlox caespitosa very large and 

 compact cushions are formed by the numerous short branches with their opposite leaves; the 

 primary root persists for several years, but increases only a little in thickness. Cushions are 

 also to be observed in some of the Compositae, for instance, Erigeron pinnatisectus (pi. 5, fig. 31), 

 and Actinella acaulis; in these the primary root is quite thick and bears a number of leafy shoots 

 with terminal inflorescences. Saxifraga bronchialis (pi. 2, fig. 11) represents a type with rela- 

 tively long branches of short internodes with the leaves imbricate, and terminated by an inflo- 

 rescence. 



In Oreoxys humilis (pi. 3, fig. 20), Mertensia alpina (pi. 5, fig. 39), and Trifolium nanum 

 (pi. 2, fig. 18), all forming compact cushions, the primary root attains a considerable length and 

 thickness, and may last for many years. The drawings represent only a small portion of the 

 cushions; we notice the thick stem parts underground, densely covered with remnants of leaves, 

 and terminated by rosettes of long-petioled leaves, and with a central inflorescence ; in Oreoxys 

 the flowering stem bends down to the ground, where the fruit matures, similar to Erigenia. 

 These three plants are able to thrive at the highest elevations in the Rocky Mountains, and 

 persist for many years. The other Alpine species of Trifolium do not show this structure, but 

 simply a slender primary root and small cushions of leafy rosettes; the inflorescence is a head 

 borne upon a long peduncle, instead of being almost sessile as in T. nanum (pi. 2, fig. 19), with 

 only two flowers. 



In some of the other Alpine types with a more or less caespitose growth the leaves are 

 somewhat crowded, but without forming compact cushions; this structure is common, and is 

 sometimes accompanied by a more or less developed rhizome, horizontal or ascending; in some 

 of these the primary root persists, in others it becomes replaced by a system of secondary- 

 roots. Lychnis montana (pi. 1, figs. 2-4) shows a strong, primary root, crowned with an open 

 rosette of leaves; at the time of flowering some vegetative shoots appear; these are, however, 

 very short, bearing only one or two pairs of leaves, and become terminated by an inflorescence in 

 the succeeding year. 



Among the Ranunculacae, Anemone narcissijlora, Caltha leptosepala, and Trollius laxus 

 have many basal leaves borne upon the very short vertical rhizome; a thick primary root of 

 quite considerable length occurs in the Anemone, while in the others the root system consists 

 of strong secondary roots when the first flowering state has been reached. In the Caltha the 



» Andersson, N. J.: Skandinaviens Cyperaceer. Stockholm, 1849. See also: Holm, Theo: Notes on Carez spectabilis Dew. (Am. Journ. 

 Sci., Vol. XLIX, March, 1920, p. 200.) 



