ii MUSCINEJEHEPATICAlMARCHANTIALES . 53 



specialised forms are found in the genus Marchantia and its 

 allies, where the antheridial receptacle is borne upon a long 

 stalk, which is a continuation of the branch from which it 

 grows, and the receptacle is a branch-system. The growing 

 point of the young antheridial branch forks while still very 

 young, and this is repeated in quick succession, so that there 

 results a round disc with a scalloped margin, each indentation 

 marking a growing point, and the whole structure being equiva- 

 lent to such a branch system as is found in Riccia or Anthoceros, 

 where the whole thallus has a similar rosette-like form. The 

 antheridia are arranged in radiating rows, the youngest one 

 nearest the margin and the eldest in the centre. In some 

 tropical species, e.g., M. geminata, the branches of the receptacle 

 are extended and its compound character is evident. 



The discharge of the spermatozoids from the ripe anther- 

 idium may take place with great force. In the case of 

 Fimbriaria Calif ornica, Peirce (i) found they were thrown 

 vertically for more than fourteen centimetres. The mechanism 

 involved includes not only the tissues of the antheridium itself, 

 but also the cells below the antheridium, and those forming the 

 walls of the chambers in which the antheridia are situated. 

 These cells, becoming strongly distended with water, exercise 

 great pressure upon the antheridium, whose mucilaginous con- 

 tents are also strongly distended. The upper wall of the 

 antheridium is finally burst, and the contents expelled violently 

 through the narrow, nozzle-like opening of the antheridial 

 chamber. 



This explosive discharge was first noted by Thuret (i) in 

 Conocephahis conicus, and has been recently studied in that 

 species by King ( i ) and Cavers ( i ) , as well as in several other 

 genera. It is much more marked in the dioecious species. 



The archegonia are never sunk in separate cavities, but 

 stand free above the surface of the thallus. The simplest form 

 may be represented by Targionia. Here the archegonia arise 

 in acropetal succession from the dorsal segments of the initial 

 cells of the ordinary branches. A superficial cell enlarges and 

 is divided as in Riccia into an outer and an inner cell. The 

 latter undergoes irregular divisions and its limits are soon lost. 

 In the outer cell the divisions occur in the same order as in 

 Riccia, but from the first the base of the archegonium is broad 

 and not tapering. Strasburger (2) states that in Marchantia 



