od8 PART IV. CLASSIFICATION. 



from the innermost layer of the amphithecium ; in the Bryinese, 

 from the external layer of the endothecium. The cells which 

 bound the archesporium on each side constitute the spore-sac. The 

 endothecial tissue which lies internally to the archesporium con- 

 stitutes the columella. In the Sphagnacese the archesporium is a 

 hollow hemisphere covering the top of the columella like a cap ; in 

 the Bryinese the archesporium is a hollow cylinder surrounding 

 the columella which extends to the apex of the capsule. In the 

 Bryinese a large intercellular space is developed in the amphi- 

 thecium, between its outer and its two inner layers ; in most 

 Polytrichacese a similar intercellular space is developed in the 

 endothecium internally to the spore-sac, between it and the central 

 portion of the columella. 



At maturity the internal cells of the capsule become dry and 

 disorganised, so that it simply contains the spores which now lie 

 loose in its cavity. It dehisces by the throwing off of its apical 

 portion as a lid or operculum in Sphaguacese and the higher 

 Bryinese (Stegocarpse) ; or it ruptures irregularly or simply decays, 

 as in the lower Bryinese (Cleistocarpse). In the higher Bryinese 

 the mouth of the dehisced capsule bears a fringe, the peristome, 

 the development and structure of which will", be described sub- 

 sequently (p. 344). 



The basal portion of the capsule, where it joins the seta, is 

 termed the neck. In the Polytrichacese the neck is considerably 

 dilated, as also in various species of Splachnum ; whilst in other 

 species of Splachnum it grows out into an umbrella-shaped struc- 

 ture. When the neck is thus markedly developed it is termed 

 the apophysis. 



The histological differentiation of the sporogonium is well- 

 marked. There is a well-defined epidermis, in which, on the 

 capsule, stomata of various forms are generally present ; either 

 scattered all over, as in the Sphagnacese ; or confined to a par- 

 ticular region of the capsule, generally the neck or the apophysis, 

 in the Bryinese. The operculum and the peristome (Bryinese) 

 show considerable complexity of structure. The structure of the 

 seta in the higher Bryinese, where alone it is elongated, very 

 much resembles that of the stem : in many forms, even in such 

 in the stem of which no central strand is present, there is a 

 central strand in the seta, marked off from the ground-tissue by 

 one or two layers of sheath-cells. In the Bryinese also, the struc- 

 ture of the neck (or apophysis) is generally characterised by the 



