Ill ^ THE JUNGERMANNIALES 73 



of lateral appendages which represent the leaves of the true 

 foliose forms. In the latter the axis is slender, and the leaves 

 usually in three rows and relatively large. 



The archegonia correspond closely in their development to 

 those of the Marchantiaceae, and in tlie lower (anacrogynous) 

 forms arise in much the same way from surface cells of the 

 dorsal part of the younger segments, and the apical cell is not 

 directly concerned in their formation. The archegonia in these 

 thus come to stand singly or in groups upon the dorsal surface 

 of the thallus, wdiose growth is not interrupted by their develop- 

 ment. In the higher leafy forms (Jungermanniacese acro- 

 gynae) they occur in groups at the end of special branches, 

 whose apical cell finally itself becomes the mother cell of an 

 archegonium, and with this the growth in length of the branch 

 ceases. 



The antheridia in most cases dififer essentially in their first 

 divisions from those of the Marchantiaceas. After the first 

 division in the mother cell, by wdiich the stalk is cut off from the 

 antheridium itself, the first wall in the latter, in all forms inves- 

 tigated except Sphcerocarpus, Riella and Geothallus, is 

 vertical, instead of horizontal, and the next formed walls are 

 also nearly vertical. The ripe antheridium is usually oval in 

 outline and either nearly sessile or provided with a long pedicel. 

 The spermatozoids are as a rule larger than in the Marchan- 

 tiales, and show more numerous coils, but like those of the lat- 

 ter, are always biciliate. 



The embryo differs in its earliest divisions from that of the 

 Marchantiacege. The first transverse wall divides the embryo 

 into an upper and lower cell, but of these the lower one usually 

 takes no further part in the development of the sporogonium, 

 but either remains undivided or divides once or twice to form a 

 small appendage to the base of the sporogonium. In the upper 

 cell the first wall may be either vertical {e. g., P cilia and most 

 anacrogynous forms), or it may be transverse. From the 

 upper of the two primary cells not only the capsule but the seta 

 and foot as well are formed. The development of these differ- 

 ent parts varies in different forms, and will be taken up when 

 considering these. 



.. - All of the Jungermanniales, except the Anelatereae, possess 

 perfect elaters, but in the latter these are represented merely by 

 sterile cells that probably serve simply for nourishing the grow- 



