THE MOSS 131 



4. Select an old sporophyte in which the spore case has 

 ripened and is open. Carefully split it lengthwise with a 

 needle, after soaking in hot water or a dilute potash solu- 

 tion, or mount entire. Note the cirtjle of teeth and cilia 

 around the opening, and the spores generally present. 

 Draw these structures. 

 I. The structure of the spore case. Make lengthwise sections 



in pith of the unopened spore case. 



1. Slices from the surface rather low down on the spore 

 case are likely to give surface views showing pores, or 

 stomata, with two guard cells. Draw. Compare these 

 structures with stomata which may have been studied on 

 the leaves of seed plants. 



2. Median sections present a cylinder of spore-producing 

 tissue (archesporium) inclosing a large pith-like region, or 

 columella. A large air space crossed by filaments lies 

 between the tissue in the interior of the spore case and 

 the outer wall (see Principles, Fig. 270, E). 



Show the structure of the median section in a semi- 

 diagrammatic figure. 



3. The histology of the spore case can best be studied in lengthwise 

 microtome sections. 



Reference. Campbell, 23. 



Questions. What are the life habits of the mosses ? Why do 

 they so frequently grow together in large tufts or mats, and 

 what are the advantages of these growth habits ? What are 

 the advantages of their erect stems and the arrangement of 

 the leaf -like scales ? What are the means of multiplication ? 

 What great advances in structure are shown by the sexual 

 organs over those of the algse ? Under what life conditions 

 are the sperms set free and the eggs fertilized ? Trace the 

 development of the egg after fertilization into the stalked 

 structure bearing the spore case. Why is this structure con- 

 sidered an asexual generation (sporophyte) distinct from a 



