VI. THE BRYALES 207 



opment can be very easily followed in longitudinal sections 

 made at this stage. The formation of the space begins at the 

 base of the capsule and proceeds toward the top. The line of 

 cells bordering on the spore-sac is very easily followed, owing 

 to their being so much larger than the neighbouring ones. As 

 this is followed down, it is found that at the base of the capsule 

 the cells are separated by large intercellular spaces, which be- 

 come less marked toward the apex. With the rapid enlarge- 

 ment of the capsule these spaces become very large, and sec- 

 tions made a little later show that during this process the cells 

 remain in contact at certain points, and form short filaments 

 that extend across the space and unite the wall of the capsule 

 with the outer spore-sac. At the base of the capsule the for- 

 mation of intercellular spaces is not confined to the single layer 

 of cells but involves the whole central mass of tissue, which be- 

 comes thus transformed into a bundle of filaments connecting 

 the columella with the basal part (apophysis) of the capsule. 

 The innermost of the two layers of cells between the arche- 

 sporium and the air-space finally undergoes a second periclinal 

 division, and in the full-grown sporogonium the archesporium 

 is bounded on the outside by three layers of cells. 



The differentiation into seta and capsule takes place late 

 in Ftinaria, and the first indication of this is the enlargement 

 of a zone between the two, forming the apophysis, which at 

 this stage (Fig. 109), is much greater in diameter than the 

 upper part of the capsule. Sections through the apophysis 

 and seta show a less regular arrangement of the cells than in 

 the sporiferous part of the capsule, but the general order of 

 cell-succession is the same, except for the formation of the 

 archesporium. Almost as soon as the capsule is recognisable, 

 the first indication of the operculum or lid becomes evident. 

 About half-way between the extreme apex of the sporogonium 

 and the top of the apophysis, a shallow depression is noticed 

 extending completely round the capsule and separating the 

 sharply conical apex from the part below. An examination of 

 a longitudinal section at this point shows that at the point of 

 separation the epidermal cells of the opercular portion are much 

 narrower than those immediately below. Examining the tis- 

 sues farther in, the archesporium is seen to extend only to a 

 point opposite the base of the operculum, and the same is true 

 of the row of large cells where the air-space is formed. If a 



