i6 MOSSES AND FERNS chap. 



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 smaller, 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 &gg. 



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 Amur a), or they are produced in a 

 special part of the ordinary thallus, which usually presents a 

 papillate appearance {e.g. FimbriarioL). 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. With 

 the exception of the Anthoceroteae, where the antheridia are of 

 endogenous origin, the antheridium, like the archegonium, arises 

 from a single superficial cell. The first division usually divides 

 the primary cell into a stalk cell and the body of the anther- 

 idium. 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 (Marchantiaceae, SpJicerocarpus) or vertical (Junger- 

 manniacese). Later, by a series of periclinal walls, a central 

 group of cells is separated from an outer single layer of cells. 

 The latter divide only a few times, and develop chlorophyll, 



