178 MOSSES AND FERNS chap. 



gonium, its structure and development correspond closely to 

 that of the other Mosses. As in these, and the acrogynous 

 Hepaticse, the apical cell of the branch becomes an archegonium, 

 and a varying number of secondary archegonia arise from its 

 last-formed segments. The mature archegonium has a mass- 

 ive basal part and long somewhat twisted neck, consisting of 

 six rows of cells. As in the other Mosses, the growth of the 

 young archegonium is apical, and probably as there the neck 

 canals are formed as basal segments of the apical cell, and the 

 ventral canal cell is cut off from the central cell in the usual 

 way. The venter merges gradually into the neck above and 

 the pedicel below^ and at maturity its wall is two or three cells 

 thick. The Qgg (Waldner (2)) is ovoid, and the nucleus 

 shows a distinct nucleolus. Whether a receptive spot is present 

 is not stated. Mixed with the archegonia are numerous fine 

 hairs like those about the antheridium. The leaves immedi- 

 ately surrounding the group of archegonia later enlarge much 

 and form a perichsetium. By the subsequent elongation of 

 the main axis both archegonial and antheridial branches are 

 often separated by the growth of the axis between them, al- 

 though at first they are always crowded together at the top of 

 the main stem. 



The Sporophyte 



Waldner (2) has recently studied carefully the develop- 

 ment of the embryo of Sphagnum, which differs essentially from 

 all the other Mosses, and has its nearest counterpart in the 

 Anthocerotes. In the species S. acutifolium, mainly studied by 

 Waldner, the sexual organs are usually mature in the late au- 

 tumn and winter, and fertilisation occurs early in the spring. 

 The ripe sexual organs are found in a perfectly normal condi- 

 tion in mid-winter, under the snow, and apparently remain in 

 this condition until the first warm days, when they open and 

 fertilisation is effected. The first embryos were found late in 

 February, and development proceeded from that time. 



The first division in the embryo is horizontal and divides it 

 into two cells. In the lower of these the divisions are irregu- 

 lar, but in the upper one the cell walls are arranged with much 

 regularity. The upper cell is the apical cell of the young em- 

 bryo, and from it, by walls parallel to the base, a series of seg- 



