BRYALES 



277 



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and the columella is in Andreaea a very 

 irregular one (Fig. 135). Further, in Archidtum, 

 which some writers put in close relation to 

 Andreaea, any cell derived from the endo- 

 thecium may apparently become a spore- 

 mother-cell. 



It is thus seen that though Sphagnum and 

 Andreaea have certain apparent characters of 

 the sporogonium in common, their segmen- 

 tation is essentially different, and the dome- 

 shaped archesporium is produced in different 

 ways in the two. It remains doubtful there- 

 fore how far the similarities indicate a real 

 affinity. In any case the relation of the 

 Andreaeales to the simpler Bryales is much 

 nearer than to the Sphagnales, and it is in 

 this direction that comparison of the sporo- 

 gonia will bring the more interesting con- 

 clusions concerning them. 



C. BRYALES. 



These include the vast majority of Mosses. 

 In their sporophyte generation there is uni- 

 formity of the general scheme, though 

 considerable fluctuation in size, as well as 

 in minor detail. Some of the smallest forms, 

 which show irregular opening of the capsule 

 on maturity, are classed as the Cleistocarpae ; 

 the more elaborate forms, which dehisce 

 transversely, setting free an operculum, are 

 designated the Stegocarpae. The latter, as 

 they represent the prevalent type in Mosses, 

 will be taken first, while the Cleistocarpic 

 forms being taken later, will then be better 

 appreciated in their value for purposes of 

 comparison. 



(a) Stegocarpae. 



The embryo of all these Mosses takes at 

 an early stage the form of a more or less 

 slender, but always simple spindle: any later 

 deviations from this are of secondary origin. 

 Its development from the zygote is first by 

 the appearance of a transverse basal wall, which is succeeded by oblique 

 segmentations in the epibasal half: these appear alternately on opposite 



Ceratodon purpureus. A, B, young 

 embryo seen from points of view at 

 right angles to one another. C = an 

 older embryo ; gg outer limit of endo- 

 thecium ; sps = outer spore-sac. (After 

 Kienitz-Gerloff.) 



