Si8 



ECOLOGY 



form as in root hairs, and (2) the observed rise of colored fluids and 

 the crystallization within the rhizoids of the Marchantiaceae of absorbed 

 salts (as Berlin blue). The special advantage of 

 the peg rhizoids, though much discussed, is not 

 known. 



Moss rhizoids. — Structure and habitat variation. 

 — Moss rhizoids commonly are brownish, branched, 

 multicellular cell filaments with oblique cross walls. 

 Often they have a rootlike aspect, by reason of 

 a strong central trunk with small lateral branches 

 (figs. 747, 748). Some mosses (as Ftinaria) de- 

 velop very long rhizoids in solutions deficient in 

 nitrogen or phosphorus. Rhizoids develop abun- 

 dantly on the aerial stems of some mosses (as Thu- 

 idium) when grown in a moist atmosphere; such 

 rhizoids are as brown as those developed in the 

 soil in spite of the exposure to light (figs. 749, 

 750). Rhizoids are developed abundantly also in 

 xerophytic mosses, and sometimes in mosses that 

 frequent running waters, while they are poorly 

 developed or wanting in pond and swamp mosses. 

 In dry soil Polytrichum juniperinum exhibits a 

 vigorous development of soil rhizoids, but in 

 swamps these are largely replaced by aerial rhi- 

 zoids ("stem felts"). Usually rhizoids are better 

 developed in erect mosses which have prominent 

 " vascular " tracts, and which grow somewhat 

 separately (as Polytrichum, Catharinea, and 

 Mnium) than in mosses without such tracts, which 

 grow in dense cushions or mats (as Leucobryum, 

 and Sphagnum, which has no rhizoids). 



Role. — Most moss rhizoids clearly are organs 

 of anchorage, though the stem felts common in 

 swamps and in moist woods are of no importance 

 in this respect. The scantiness of experimental 

 data makes it impossible to speak in general terms 

 concerning the efficiency of the rhizoids in absorption. Probably 

 mosses like Polytrichum, which grow as detached individuals and pos- 

 sess "vascular ''strands and extensive rhizoids, are able to absorb water 



Fig. 748. — A moss 

 rhizoid with its 

 branches; note the ob- 

 lique cross walls, im- 

 mediately above which 

 branch rhizoids origi- 

 nate at a definite posi- 

 tion ; highly magnified. 



Figs. 749, 75°- — 

 Aerial rhizoids: 749, a 

 swamp moss as ordi- 

 narily observed; 750, 

 the same individual after 

 several days in a moist 

 chamber. 



