292 PLANT SOCIOLOGY 



these. Rosette plants are distributed over the temperate zones of the 

 earth but also extend to the subtropics in considerable numbers. 



c. Hemicryptophyta scaposa (scapose plants): mostly tall herbs, rarely 

 grasses, usually with a solid taproot and with a more or less leafy stalk. 

 The bottom rosette of leaves may be lacking as in Thalictrum, Hypericum, 

 Onohrychis, Ejnlobium, and Gentiana or present as in Ranunculus, 

 Geranium, Campanula, and Phyteuma. Many of the common meadow 

 and woodland plants of Eurasia and North America are scapose plants. 



d. Hemicryptophyta scandentia (climbing plants): hardy plants with 

 annual climbing stems and renewal buds at the base. They are especially 

 common in the warmer parts of the temperate zone and include species of 

 Convolvulus, Astragalus, Vicia, and Lathyrus. 



VIII. CHAMAEPHYTEs (surfacc plants): with renewal buds above the surface 

 of the earth; the plants enjoy only such protection as is afforded by the plant 

 itself, either through protective mechanisms on the bud or by dense growth or by 

 dead shoots. Important subgroups are: 



1. Bryochamaephyta reptantia (carpet mosses): creeping carpet mosses such 

 as Hypnum, H ylocomiujn, and Leucodon, which lie loosely upon the sub- 

 stratum and often form large beds. 



2. Chamaephyta lichenosa (fruticose lichens): lichens, whose thalli often 

 reach a height of 10 cm. and more, distributed as independent forms 

 more especially in regions with cold winters, where they cover large areas 

 either on forest soils or in open country. They are sensitive to changes 

 in the moisture of the air, but in general they can bear low temperatures and 

 severe wind without much harm. E. Frey (1922, p. Ill) distinguishes 

 three forms: (1) the Cetraria form (C islandica, C. nivalis, C. cucullata, 

 Ramalina strepsilis) ] (2) the Cladina form (Cladonia rangifcrina, C. 

 alpestris, C. silvatica, Alectoria ochroleuca); (3) the Usnea form (Thamnolia 

 vermicularis) . In humid regions Bryochamaephytes and Chamaephyta 

 lichenosa frequently live epiphytically. 



3. Chamaephyta reptantia (creeping herbs) (Fig. 148 a): herbaceous plants 

 with creeping or ascending shoots, which survive the unfavorable season 

 and bear the renewal buds. These actively creeping herbs such as Trifolium 

 repens, Thymus serpyllimi, Veronica officinalis, and Linnaea borealis often 

 send out roots, a phenomenon which rarely occurs in the passively creeping, 

 negatively geotrophic forms such as Carex limosa, C. chordorrhiza, Cerastium 

 latifolium, C. strictum, C. tomentosum, and Stellaria holostea. Within a 

 subform are to be classed the ascending creeping grasses of subtropic regions 

 (Brachypodium ramosum, Oryzopsis) whose perennating shoots, 19 to 20 

 cm. high and sometimes higher, carry the plant through the unfavorable 

 season. These sometimes develop into lianas. 



4. Chamaephyta succulenta (leaf succulents): succulent-leaf perennials with 

 water-storing tissues, which enable them to weather continued dryness. 

 They are especially characteristic of arid climates, xeric habitats, rock, 

 rubble, and sand substrata. The genera Sedum, Umbilicus, and Sempervi- 

 vum offer numerous representatives of this group. 



5. Chamaephyta pulvinata (cushion plants): with negatively geotrophic 

 and densely crowded shoots so that typical cushions resemble a shield 

 with upraised center. The center of the cushion (polsters) filled with 



