126 MCALLISTER: MORPHOLOGY OF THALLOCARPUS 
FIG A later stage in the development of the embryo. Venter wall two cell 
layers in thickness. A group of cells at the apex of the sporophyte separated from 
the main mass 
I Embryo about half grown. No distinction visible between the periph- 
eral ells and the inner cells of the sporophyte 
- Ii. Peripheral cells of iciitebbivke now easily identified by their scanty 
ROB content 
Fr Geatinteation of the cell walls and the rounding up of the spore mother 
cells. Cells of the amphithecium still plump and intact. 
Fic. Spore mother cells fully rounded up and surrounded by the homoge- 
neous napa material. Peripheral layer of cells disintegrated. Venter cells 
still in 
14. Spores approaching maturity. The papillate retaining wall of the 
Hight pa nearly mature. The spore walls still thin. 
G. 15. One spore and part of the common retainin ng wall. 
ee 16. Section of nearly mature spore, pulled away from spore ball by sec- 
tioning knife. 
