l8o PRACTICAL BOTANY 



head or theca is supported on a long stalk, or seta. Note in 

 specimens which are not too ripe 



a. The calyptra, a dry fibrous hood, covering the apex of the 

 sporogonium : beneath this is 



b. The lid-like operculum with its terminal beak : this lid 

 may be easily detached, disclosing 



c. The pale-grey epiphragm, which appears as a transverse 

 membrane, attached at its margin to the capsule by a number 

 of short teeth of the peristome. 



d. At the base of the theca observe a swelling called the 

 apophysis. 



e. By carefully removing the leaves from the apex of a plant 

 which bears a sporogonium, it may be seen that the base of the 

 seta is enveloped by a closely fitting sheath, the veil or vaginula, 

 the origin of which will be explained later. 



. MICROSCOPIC INVESTIGA TION. 

 Oophyte Generation. 



II. Cut transverse sections of a mature stem of Polytrichum: 

 mount some in glycerine, others in chlor-zinc-iodine, or in 

 iodine solution : examine them first under a low power, and 

 observe in those mounted in glycerine 



1. The outline of the section, which is usually more or less 

 clearly triangular. 



2. The dense reddish-brown band of peripheral sclerenchyma, 

 which passes over gradually into 



3. A broad, thinner-walled band of tissue, which may be 

 termed the cortex : this finally surrounds 



4. A central mass of firm, yellow-walled tissue. 



Examine these several tissues in detail, under a high power>. 

 and observe that 



1. At the extreme outer limit is a thin cuticle, with small and 

 irregular outgrowths : there is no clearly defined epidermal layer. 



2. The peripheral sclerenchyma consists of cells with clearly 

 stratified red walls, which are of such thickness as almost to 

 obliterate the cell-cavity. 



