VI. 



THE DRY ALES 



219 



of structure. Tctraphis pcUucida is a small Moss, which at 

 the apex of its vegetative branches bears peculiar receptacles 

 containing multicellular gemnicC of a very characteristic form. 

 The leaves that form the receptacle are smaller than the stem 

 leaves, and closely set so as to form a sort of cup in which the 

 gemmse are produced in large numbers. These arise as slender 

 multicellular hairs, the end cell of which enlarges and forms a 

 disc, at first one-layered, but later, by the walls parallel to the 

 broad surfaces, becoming thicker in the middle, and lenticular 



Fig. 118. — Tctraphis pellucida. A, Plant with gemmae, X6; B, upper part of the 

 same, X50; C, young gemma, X600; D, a fully-developed gemma, X300. 



in form. The arrangement of the cells in the young gemm?e 

 looks as if the growth of the bud was due to a two-sided apical 

 cell (Fig. 118, C), but this point was not positively determined. 

 These gemmse give rise to a protonema of a peculiar form, from 

 which in the usual way the leafy stems develop. The proto- 

 nemal filaments grow into flat thalloid expansions that recall 

 those of Sphagnum and Andrecca. 



