SPHAGNALES 273 
of tissue with rounded apex (Fig. 133 F, H). The peripheral series of 
cells, or amphithecium, divides periclinally to give off internally the single 
Development of sporogonium of Sphagnum acutifolium, Ehrh. A=embryo with four 
tiers; s=apical cell; 4=basal cell with oblique division. B=embryo with five tiers. 
C=optical section of the same embryo; one quadrant is still undivided ; a=anticMnal ; 
f=periclinal walls; 4=principal walls. -=transverse section of the lower part of an 
embryo. =a rather older stage; sf7=spore-forming layer. /=median longitudinal 
section of a sporogonium showing the bell-shaped sporogenous layer, and the wall covering 
it externally. G=transverse section of a sporogonium of similar age; lettering as in & 
//=median longitudinal section, though a half-ripe sporogonium ; ca/=calyptra; spr= 
spore-cavity, in which the spore-mother-cells are isolated ; sfs=spore-sac ; ¢f7 = epidermis}; 
et=furrow in wall where the operculum will separate ; Ps=pseudopodium ; v7=vaginula ; 
pbl=perichaetial leaves ; co/=columella. (After Waldner, from Engler and Prantl.) 
layer of the archesporium; this appears as a continuous dome closely 
investing the columella. The external product of the amphithecium forms 
s 
