28 PRACTICAL BOTANY. 



2. The amphigastria and rhizoids attached to the 

 lower surface. 



3. The cavities in the tissue, of two sorts, both 

 opening by narrow mouths on the upper surface 



a. Air-cavities fundamentally similar to those 

 of the vegetative thallus, with a "stoma" 

 above the centre of each, and with chloro- 

 phyll-containing cells as before. 

 I. Flask-shaped cavities each containing one 

 antheridium : these also open by a narrow 

 channel on the tipper surface of the disk. 

 Look for a single ripe antheridium which has been 

 cut through longitudinally : having found one, examine 

 it in detail under a high power, and observe 



1. The short stalk by which it is attached to the 

 base of the cavity. 



2. The wall of the antheridium, consisting of a single 

 layer of thin-walled cells. 



3. The mother-cells of the antherozoids of cubical 

 form, and small size, which together constitute a dense 

 central mass. 



Trace the channel of one of the flask-shaped cavities 

 up to the surface of the thallus, and note that the 

 structure of the pore is quite distinct and different from 

 that of the " stoma." 



Compare antheridia of various ages in sections cut from 

 younger male branches : by such a comparison it may be ascer- 

 tained that each, antheridium arises from a single cell at the base 

 of the flask-like cavity : trace the successive divisions which 

 accompany the development of one such single cell into the mature 

 antheridium. 



Cut tangential sections from the upper surface of a male branch, 

 and under a high power note 



