428 SOUTH Ai-KICAX HKrATlC.K. 



to have important functions in connection with the absorption 

 of water and mineral sahs. 



Be this as it nia\ , these tuberculate rhizoids, though usually 

 produced on the under-surface of the thallus, extend in some 

 cases from the common receptacles of the fructitication down 

 special almost enclosed grooves in tlie peduncle, and along the 

 under-surface of the thallus t(j the ground-suriace — a distance 

 occasionally of two inches — whicli is held to be a proof that in 

 these cases the i)eduncle is an ad;'.])tation of part of the thallu> 

 itself to a special jjurpose. 



In certain am])hil)ious Riccicc rhizoids occur on the land 

 form but not on the floating form, where there is no use for 

 them, and on R. nutans they are replaced on the floating form 

 by })rotective flat, serrate scales containing chlorophyll and act- 

 ing as leaves. 



In the case of epiphytic species the rhizoids are sometimes 

 forked and discoid at the end. for the puq^ose of adhesion. 



These rhizoids frequently occur in the mo-^t unnatural 

 positions, thus in Ditinorticra. which grows almost in water. 

 they occur on the under->urface of the stalked common recep- 

 tacle, and are specially protected in channels sunk into the 

 peduncle down to the ground ; in many Lejeunece tiiey are 

 grouped on a wart i)roduced on the outer surface of the foliole, 

 and in RaduUi the rhizoitl-producing wart occurs on the infolded 

 lobule of the leaf. The more frcfjuent position, however, is on 

 the under-surface of the >tem. either toward its base only, or 

 occasionally along its entire length, and especiallx in etiolated 

 flagelliferous portions. 



The ITepaticre, having no true roots, are usually epiphytes, 

 and often adhere very tenaciously, by means of the terminal 

 discs of their rhizoids, to mosses, tree-bark, stones, or other 

 hepatics. 



They are not known to be parasites, and ])robabl\- never are 

 so ; they are always chloronhyllose. and the chemical ^alts neces- 

 sary for their nutriment thc\' are al)le to absorb directlx', with 

 water, over their surfaces, so that the i)urpose of the rhizoids 

 is, in part at least, the fixation of the ])lant to its host or site; 

 on the other hand, the greater vigour of an undisturlied patch 

 com])ared with that of an adjoining patch which has been more 

 or less detached, shows that either the rhizoids al)'^orl), or they 

 keep the olant in such close contact with the host or site as to 

 render absori^tion easy. 



There are certain thalloid tienera in wliich water is not 

 absorbed bv the ui)per surface of the thallus, but rhizoids occur 

 on all parts of its under-surface. connecting with central com- 

 mon strands reaching the ground surface. wherei)\ irrigation 

 of the whole thallus is maintained by the rhizoids and by 

 capillaritv between them, apart from the usual osmotic circu- 

 lation within the plant. 



The special contri\ances found in thi> i^rou]) for tlie reten- 



