124 STUDY OF COMMON PLANTS. 



moved, the peristome, or circle of teeth surround- 

 ing the opening of the capsule. The peristome 

 presents a widely different appearance in the 

 different genera, and its structure requires careful 

 study. It consists of four, eight, sixteen, thirty- 

 two, or sixty-four teeth, plain, or variously cut and 

 ribbed, and often very hygroscopic. In a few 

 genera the peristome is wanting. 



4. Within the capsule, the spores filling a cylindrical 



space which surrounds a central mass of tissue 

 called the columella. 



5. In some mosses, besides the parts already named, 



there are to be observed the epiphragm, a thin, 

 membranaceous structure, stretching across the 

 mouth of the capsule; and at the base of the 

 capsule a swelling called the apophysis. 



Note. — The structure of the capsule should be studied in detail 

 in a number of different mosses, and descriptions accompanied 

 by careful drawings should be written. The peristome, especially, 

 is very characteristic and furnishes important features for the sys- 

 tematic study of the group. 



Protonema. 



If ripe spores are sown on moist soil, or on a compact 

 clump of moss, and kept under a bell-jar at the temperature 

 of an ordinary living room, the early stages of develop- 

 ment of the protonema are easily observed. The spore 

 swells and pushes out a papilla which elongates into a 

 tubular cell. This increases in length, becomes septate, and 

 branches are formed. 



The later stages of development may be followed out 

 with the same material ; but there are some advantages in 

 obtaining vigorous specimens by the simple expedient of 

 turning a clump of moss bottom side up, and keeping it in 



