352 PKACTICAL BOTANY 



in such cases the spores would be almost mature : the structure 

 of the whole capsule would accordingly be more difficult to 

 understand than in the younger specimens. 



Observe 



1. The seta, which widens out gradually into 



2. The theca or capsule, without any clearly 

 marked basal swelling, or apophysis : at the apex of 

 the theca observe that the section has traversed 



3. The operculum or dome-like lid : beneath this 



4. The yellow or orange peristome : in the lower 

 part of the capsule note 



5. The outer wall consisting of a clearly marked 

 epidermis, and beneath it some three or four layers of 

 thin-walled parenchyma. 



6. The air-space, traversed obliquely by filaments 

 of thin-walled cells, suspending a central mass con- 

 sisting of 



7. The spore-sac, which will be seen to be composed 

 of two or three layers of thin-walled cells. 



8. A layer of spore-mother-cells, recognized by 

 their dense protoplasmic contents. 



9. The central mass of thin-walled tissue of the 

 columella, which extends upwards into the concave 

 operculum. 



By careful observation of longitudinal sections under 

 a high power the following points may be verified : 



1. That stomata occur in the epidermis towards 

 the base of the sporogonium. 



This may be confirmed by cutting tangential sections from the 

 base of the sporogonium, in which the stomata, with their two 

 guard-cells, may be clearly seen in surface view. 



