i6 MOSSES AND FERNS chap. 



cell develop archegonia at once, and finally the apical cell itself 

 becomes the mother cell of the last-formed archegonium, and, 

 of course, with this the growth in length of the branch ceases. 

 With the exception of the Anthocerotes, where the arche- 

 gonium mother cell does not project at all, it quickly assumes 

 a papillate form and is divided by a transverse wall into a basal 

 cell, and an outer one from which the archegonium itself 

 develops. The divisions in this outer cell are remarkably 

 uniform. Three vertical walls are first formed, intersecting so 

 as to enclose a central cell (Fig. 2, G). In this central cell a 

 transverse wall next cuts off a small, upper cell (cover cell) 

 from a lower one. Subsequently the three (or in the 

 Jungermanniacese usually but two) first- formed peripheral 

 cells divide again vertically, and by transverse walls in all of 

 the peripheral cells, and somewhat later in the central one also, 

 the young archegonium is divided into two tiers, a lower one 

 or venter, and an upper one, the neck (Fig. 2, F). The middle 

 cell of the axial row, by a series of transverse walls, gives 

 rise to the row of neck canal cells, and the lowermost cell 

 divides into two an upper one, the ventral canal cell, and a 

 larger lower one, the egg. 



The antheridium shows very much greater diversity in its 

 structure, and equally great difference in its position. The 

 origin in the thallose forms is usually the same as that of the 

 archegonium, and indeed where the two grow mixed together, 

 as in many species of Riccia, it is sometimes difficult to 

 distinguish them in their earliest stages. Usually, however, 

 the antheridia are borne together, either on special branches 

 {Marchantia, species of Aneura), or they are produced in a 

 special part of the ordinary thallus, which usually presents a 

 papillate appearance (e.g., Fimhriaria) . In the foliose Junger- 

 manniacese the antheridia are often borne singly in the axils 

 of slightly modified leaves, but in no case does the apical cell 

 of the shoot become transformed into an antheridium. The 

 antheridium, like the archegonium, arises from a single super- 

 ficial cell. The first division usually divides the primary cell 

 into a stalk cell and the body of the antheridium. The first 

 may remain very short and undergo but few divisions, or it 

 may develop into a stalk of considerable length. The first 

 division in the upper cell may be either transverse (Marchan- 

 tiacese, Sphcorocarpus) or vertical (Jungermanniacese). 



