II MUSCINEM— HEPATIC^— MARCHANTI ALES 65 



The elaters are at first elongated thin-walled cells with a 

 distinct although small nucleus, and nearly uniformly granular 

 cytoplasm. As they grow the cytoplasm loses this uniform 

 appearance, and a careful examination, especially of sections, 

 shows that the granular part of the cytoplasm begins to form 

 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 cyto- 

 plasm, 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 Fimbriaria 

 until maturity. 



The differences in the structure of the sporogonium in 

 dififerent genera of the Marchantieae are slight. In Marchantia 

 polymorpha, 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 Jungermanniaceae, is 

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

 young embryo develops into the capsule, but in Fimbriaria 

 Calif ornica 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. 25, C). 



When ripe, the cells of the capsule-wall in Targionia de- 

 velop upon their walls dark-colored annular and spiral thicken- 

 ings much like those of the elaters. These thickenings are 

 quite wanting in Fimbriaria. 



The dehiscence of the capsule is either irregular, e.g.. 

 Targionia, or by a sort of lid, e.g., Grimaldia, or by a number 

 of teeth or lobes, e.g., Lumilaria, Marchantia. In some forms 

 after fertilisation there grows up about the archegonium a cup- 

 shaped envelope, "perianth, pseudoperianth," which in Ftm- 

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