S8 MOSSES AND FERNS chap. 



its ventral surface it shows a furrow in which rhizoids are 

 produced in great numbers, and this furrow continues along 

 the ventral surface of the thallus. 



The highest type is that of Leitgeb's ^'Compositse." In this 

 form the female receptacle is a branch system similar to that 

 of the male receptacle of Marchantia. The branching is usually 

 completed at a very early period, while the receptacle is almost 

 concealed in the furrow in the front of the thallus. A simple 

 case of this kind is seen in Fimhriaria Calif ornica (Fig. 21). 

 In this case there are four growing points that have arisen from 

 the repeated dichotomy of the primary growing point of the 

 branch, and each of these gives rise to archegonia in acropetal 

 succession, much as in Targionia, but the number of archegonia 

 is small, not more than two or three being as a rule formed from 

 each apex. The development of the dorsal tissue is excessive 

 and the ventral growth reduced to almost nothing, and the 

 growing apices are forced under and upward and lie close to 

 the stalk, and the archegonia have the appearance of being 

 formed on the ventral side of the shoot, although morphologic- 

 ally they are dorsal structures. In the common Marchantia 

 polymorpha the branched character of the receptacle is empha- 

 sised by the development of the "middle lobe" between 

 the branches. These lobes grow out into long cylindrical 

 appendages between the groups of archegonia, and give the 

 receptacle a stellate form. Usually in M, polymorpha there 

 are eight growing points in the receptacle, and of course as 

 many groups of archegonia, which are more numerous than in 

 any other genus, amounting to a hundred or more in one recep- 

 tacle. In Marchantia, as well as some other genera with com- 

 pound receptacles, there are two furrows in the stalk, showing 

 that the latter is influenced by the first dichotomy. While the 

 archegonia, before fertilisation, are quite free, the whole group 

 of archegonia, and indeed the whole receptacle, is invested with 

 hairs or scales of various forms that originate either from the 

 epidermis of the dorsal side, or as modifications of the ventral 

 scales. 



The peculiar American genus Cryptomitrium has been 

 investigated by Abrams ( i ) and Howe (3), who finds the devel- 

 opment of the carpocephalum to agree essentially with that of 

 Fimhriaria Calif ornica. Cavers (6, 7, 8), has recently investi- 

 gated that of Conocephalus {Fegatella), Reboulia and Preissia. 



