ROOTS AND RHIZOIDS 



519 



and salts through the latter; indeed, the rise of colored liquids -has 

 been witnessed in the rhizoids of Polytrichum. When the rhizoids of 

 Catharinea are severed in the soil, the leaves wither precisely as they do 

 in seed plants when the roots are cut. Water drops appearing on cut 

 stem surfaces of Mnium 

 have been supposed to 

 indicate conduction and 

 hence rhizoid absorp- 

 tion. In Polytrichum 

 and in Catharinea the 

 rhizoids are intertwined 

 like the strands of a 

 rope, so that doubtless 

 water can ascend be- 

 tween them by capillar- 

 ity as well as within 

 them. In mat and 

 cushion mosses it is prob- 

 able that leaf absorp- 

 tion, facilitated by the 

 ready capillarity made 

 possible by close con- 

 tact between adjoining 

 shoots, is muchsmore im- 

 portant than is rhizoid 

 absorption (p. 611). 



Rhizoids of algae and 

 of lichens. Algae. 

 Many small algae are 



entirely Unattached, and FIG. 751. A marine alga (Nereocystis), showing a 



move actively (Volvox) rhizoid complex or system f hap f ra ; which s ? ves f 8 



J ' a holdfast organ, fixing the plant firmly to a rocky sub- 



or drift passively (Pleu- stratum below sea level; note the stalk or stipe, whose 

 TOCOCCUS). Other forms bladder-like expansion floats the leaflike organs at the 



are attached by the muci- water surface ' ~ From CouLTER (Part I} ' 

 lage they exude. Some filamentous algae (as Ulothrix and Oedogonium) 

 are anchored by the basal cell, which may differ from the other cells in 

 shape and color ; such forms often are epiphytic on other water plants. 

 Rootlike rhizoids occur in Vaucheria, Botrydium, and Chara. Large 

 marine algae are attached to rocks by much-branched rhizoids (or 



