126 TYPE STUDIES 



THE MOSSES, OE MUSCI 



127. Sphagnum, the peat moss. Study the life habits, tufted growth, and 

 ability to absorb water. Explain the latter property after a study of the 

 cell structure. 



A. General morphology. Note : 



1. The main stem. 



2. The lateral Iranches. Compare their arrangement at the top of the 

 stem and below in a species that grows up into the air. What two 

 forms of branches are present and what are the factors that deter- 

 mine their direction of growth ? 



3. The leaf -like scales or leaves. 

 Illustrate these points in a habit sketch. 



B. Vegetative structure. Tease out the tip of a branch and obtain the 

 youngest leaves possible. Compare their structure with that of the 

 mature leaf. Make a series of drawings under h.p., showing this cell 

 structure in young and old leaves. They should make clear : 



1. The significance of the large empty cells, tracAeJds, found in the 

 older leaf-like scales. What is the structure of these cells with 

 their rib-like thickenings and large circular openings ? Trace their 

 development from the cells of young scales. 



2. The structure of the green framework which surrounds the empty 

 cells in old leaves. Of what is the framework composed ? Trace 

 its development from the cells of young scales. 



3. Examine the cell structure of the stem. Are empty cells, tracheids, 

 found there ? 



C. The sexual organs, antheridia and archegonia. These are so rarely 

 found, since they are generally formed early in the spring or late in 

 winter, that their study is not practicable in a general course. 



D. The sporophyte. Note the groups of sporophytes, also called fruits of 

 the moss, situated at the tips of the tufted branches. Make a habit 

 sketch. Study : 



1. The large globular spore case, opening by a lid, and situated at the 

 end of a rather thick column (pseudopodium). 



2. Lengthwise sections will show that the column is not a part of the 

 sporophyte but an outgrowth from the gametophyte. The sporo- 

 phytes have no stalk but are attached to the column by a large foot 

 (see Principles, Fig. 260, E). The spores are developed in a dome- 

 shaped spore-producing tissue (archesporium). Draw characteristic 

 features of the sporophyte in detail. 



Keferbnce. Campbell, 23. 



