64 MOSSES AND FERNS chap. 



a spiral band, recalling somewhat the chlorophyll band of 

 Spirogyra. This is the beginning of the characteristic spiral 

 thickening of the cell wall, and while at first irregular, the 

 arrangement of the granular matter becomes more definite, and 

 following the line of this spiral band of granules in the 

 cytoplasm, there is formed upon the inner surface of the wall 

 the regular spiral band of the complete elater. This band, 

 which is nearly colourless at first, becomes yellow in the mature 

 elater, and in Targionia, where there are generally two, they are 

 almost black. Not infrequently branched elaters are found, 

 but these are unicellular, and no doubt owe their peculiar form 

 to their position between the spore mother cells in the young 

 archesporium. An axial row of granules, which seem to be of 

 albuminous nature, remains in the elaters of Fivibriaria until 

 maturity. 



The differences in the structure of the sporogonium in 

 different genera of the Marchantieae are slight. In Marchantia 

 polymorpJia, the young sporogonium is nearly globular, and even 

 when full grown it is ellipsoid with the stalk and foot quite 

 rudimentary. Most forms, however, have the foot large, but 

 the stalk, compared with that of most Jungermanniacese, is 

 short. In most of them the whole of the upper half of the 

 young embryo develops into the capsule, but in Fimbriaria 

 Californica I found that the archesporium was smaller than in 

 other forms described, and that sometimes the apical part of 

 the sporogonium was occupied by a sort of cap of sterile cells- 

 (Fig. 23). 



The dehiscence of the capsule is either irregular, eg. 

 Targionia, or by a sort of lid, eg. Grimaldia, or by a number 

 of teeth or lobes, eg. Lunularia, Marchantia. In some forms 

 after fertilisation there grows up about the archegonium a cup- 

 shaped envelope, " perianth, pseudoperianth," which in Fimbriaria 

 especially is very much developed, and projects far beyond the 

 ripe capsule (Fig. 19). 



The germination of the spores corresponds in the main with 

 that of Riccia. Except in cases where the exospore is very 

 thin, in which case it is not ruptured regularly, the exospore 

 either splits along the line of the three converging ridges upon 

 the ventral surface, and through this split the endospore 

 protrudes in the form of a papilla, as in Riccia ; or in Targionia 

 (Fig. 25) the exospore is usually ruptured in two places on 



