350 PRACTICAL BOTANY 



its apex, while the lower portion remains as an investment of the 

 base of the seta, and is called the veil or vaginula. 



Note especially in young sporogonia the two-sided, wedge- 

 shaped apical cell, with segments cut off from either side. 



Sporophyte Generation 



The Sporogonium 



X. Having noted the external characters of the 

 sporogonium of Polytrichum, as above described, 

 cut transverse sections of the mature seta : mount in 

 glycerine or glycerine jelly. Being a cylindrical organ 

 the transverse section is circular. Note 



1. The superficial layer of cells with a definite cuticle 

 and thick yellow walls. 



2. A band of brown sclerenchyma, which graduates 

 internally into 



3. A thin-walled parenchyma, with large inter- 

 cellular spaces, and containing chlorophyll. 



4. Centrally is a strand of denser tissue without 

 intercellular spaces. 



XI. Cut median longitudinal sections of the base of 

 the seta, which is inserted on the apex of the Moss-plant 

 or oophyte : mount as before, and note in the upper 

 part of the seta the superficial layer, brown scleren- 

 chyma, thin-walled parenchyma, and central strand, as 

 above described. Following the seta down to the base, 

 it will be seen that the cuticle and brown sclerenchyma 

 stop short, and are replaced by thin-walled parenchyma 

 with plentiful protoplasm ; this tissue of the sporophyte 

 is in close connection with the inner surface of the 



