52 MOSSES AND FERNS chap. 



usual way. The free spermatozoid (Fig. 15, D) shows about 

 one and a half complete turns of a spiral. The cilia are very 

 long, and the vesicle usually plainly evident. 



When the antheridia are borne directly upon the thallus, 

 the apical growth continues after antheridia cease to be formed, 

 and the receptacle is thus left far back of the growing-in point. 

 In forms like Targionia, however, where there are special 

 antheridial branches, the growth of these is limited, and gener- 

 ally ceases with the formation of the last antheridia. The most 

 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 equivalent 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 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^ states that in 

 Marchantia there is a division of the outer of the two primary 

 cells by a wall parallel to the first, and that the lower one 

 forms the foot of the archegonium, and Janczewski " gives the 

 same account of the young archegonium of Preissia commutata. 

 This certainly does not occur in Targionia, and to judge from 

 the later stages of Finibriaria Californica, this species too lacks 



^ Strasburger (2), p. 416. ^ Janczewski (i), p. 3S6. 



