CH. II MUSCINE^— HEPATIC^— MARCHANTIALES 9 



phyll, and therefore capable of entirely independent growth. 

 No true roots are found, but rhizoids are generally present in 

 great numbers, and these serve both to fasten the plant to the 

 substratum and also to supply it with nutriment. 



The form of the gametophyte varies much. In the simplest 

 HepaticEe, like Aneura and Pellia, it is a flat, usually dichoto- 

 mously branched thallus composed of nearly or quite uniform 

 cells, without traces of leaves or other special organs. From 

 this simplest type, which is quite like certain Algae, dififerentia- 

 tion seems to have proceeded in two directions; in the first 

 instance the plant has retained its thallose character, but there 

 has been a specialisation of the tissues, as we see in the higher 

 Marchantiacese. In the second case the differentiation has 

 been an external one, the thallose form giving place to a dis- 

 tinct leafy axis. This latter form reaches its completest 

 expression in the higher Mosses, where it is accompanied by a 

 high degree of specialisation of the tissues as well. The 

 growth is usually from a single apical cell, which varies a good 

 deal in form among the thallose Hepaticas, but in the foliose 

 Hepaticse and Mosses is with few exceptions a three-sided 

 pyramid. 



The gametophyte of the Muscineas frequently is capable of 

 rapid multiplication, which may occur in several ways. Where 

 a filamentous protonema is present this branches extensively, 

 and large numbers of leafy axes may be produced as buds from 

 it. Sometimes these buds are arrested in their development 

 and enter a dormant condition, and only germinate after a 

 period of rest. Another very common method of multiplica- 

 tion is for the growing ends of the branches of a plant to 

 become isolated by the dying away of the tissues behind them, 

 so that each growing tip becomes the apex of a new plant. 

 Very common in the Hepaticse, but less so in the Mosses, is the 

 formation of gemmae or special reproductive buds. These are 

 produced in various ways, the simplest being the separation of 

 single cells, or small groups of cells, from the margins of the 

 leaves. In the case of Aneura multvUda they are formed within 

 the cells and discharged in a manner that seems to be identical 

 with that of the zoospores of many Algse. Again, multicellu- 

 lar gemmae of peculiar form occur in several of the Hepaticse, 

 e.g., Blasia, Marchantia, where they occur in special receptacles. 



