V. MOSSES (MUSCI): SPHAGNALES—ANDREJEALES 185 



and left — in short, lias the character of the familiar ''two-sided" 

 apical cell. Tlie numher of segments thus formed ranges from 

 eleven to thirteen. Each segment is first divided by a vertical 

 median wall into equal parts, so that a cross-section of the 

 young embryo at this stage shows four equal quadrant cells. 

 The next divisions correspond to those in Sphagnum, and result 

 in the separation of the endothecium and amphithecium. The 

 formation of the archesporium, however, differs from Sphag- 

 num, and is entirely similar to that of the higher Mosses. In- 

 stead of arising from the amphithecium as in the former, the 

 archesporium is formed by the separation of a single layer of 

 cells from the outside of the endothecium. All of the segments 

 do not form spores, but only three or four, beginning with the 

 third from the base. The two primary segments of the upper 

 part of the embryo, like the corresponding ones in SpJiagnnin, 

 go to form the foot, which is not so well developed, however, 

 as in the latter. The originally one-layered archesporium later 

 becomes double, and as in Sphagnum extends completely over 

 the columella, which is thus not continuous with the tissue of 

 the upper part of the sporogonium. As in Sphagnum also, no 

 trace of the intercellular space formed in the amphithecium of 

 the Bryales can be detected. A section of the nearly ripe cap- 

 sule shows the club-shaped columella extending nearly to the 

 top of the cavity. With the growth of the capsule the space 

 between the inner and outer spore-sacs becomes very large to 

 accommodate the growth of the numerous spores. The pseu- 

 dopodium is exactly the same as in Sphagnum, and the vaginula 

 and calyptra are present. The latter is much firmer than in 

 Sphagnum, and like that of the Bryales. 



Archidium 



The genus Archidium is one whose systematic position has 

 been long a subject of controversy. It has usually been associ- 

 ated with the so-called cleistocarpous Bryales, but the researches 

 of Leitgeb ( 8) seem to point to a nearer affinity with Andrccca. 



The species of Archidium are small Mosses growing on the 

 earth, and especially characterised by the small number, but 

 very large size, of the spores contained in the sessile globular 

 sporogonium. Hofmeister ( ( i ) , p. 160) , was the first to study 

 the development, and his account agrees in the main with Leit- 



