114 



MORPHOLOGY 



ing in function the suppressed seta. It is formed by the elongation 

 of the axis of the leafy branch beneath the sporophyte, and as it bears 

 the capsule at its summit, it resembles an ordinary elongated seta (fig. 



250). Of course the foot of the sporophyte 

 is embedded in its tip. 



Conclusions. — The Sphagnales present 

 a remarkable mixture of liverwort and 

 moss characters. The simple thallus 

 bod y of the gametopT ]jte.iSae mbies th at 

 of the anacrog3mous Jungerm annia les; 

 the^ecial leafy sFx^^^BrancKes su^est^the 

 aLi'Ogyaous Jungermanniales ; while the 

 spofoph)rte is organized as in the Antho- 

 cerotaleT. On the other hand, the erect 

 leafy branches of the gametophyte and 

 the operculum of the sporophyte are both 

 distinctly moss characters. In addition to 

 these characters in common with liver- 

 worts and true mosses. Sphagnum possesses 

 Fig. 2^o.-Sphasnum: sporo- ^^j^^^. characters pecuhar to itself. 



phyte, showing the globular cap- * 



sule with operculum (lid) and It was remarked that the simplest con- 

 dome-shaped mass of sporogenous ceivable liverwort would be produced by 

 tissue (in tetrad stage), the very combining the gametophyte of Pellia^yii\i 

 short neckhke seta, the bulbous ° ° . . „ . 



foot embedded in the apex of the the sporophyte of Rtccta. So m produc- 

 leafy axis (gametophyte), which is ing Sphagnum, One might imagine a corn- 

 extended beyond the leaves to ^ination of the gametophytes of the two 

 form the stalkhke (seta-hke) ° 5, . , , 



pseudopodium. groups of Jungermanniales with the spo- 



rophyte of Anihoceros. 



The features of Sphagnum that distinguish it from true mosses in 

 general are (i) the thallose gametophyte, (2) the axillary aji theridia, (3) 

 the dome-shaped sporogenous tissue derived from the amphithecium, 

 and (4) the pseudopodium. 



Such a form is often called a transition form, but better a synthetic 

 form, for it combines the characters of several groups. 



(2) Andreaeales 



General character. — This group comprises a single genus (Andreaea) of sili- 

 ceous rock mosses. Sphagnum is hydrophytic, but Andreaea is very xerophytic. 



